Lord Snowdon, former husband to Princess Margaret, has died peacefully aged 86.
He worked as a photographer, and his former agency confirmed the news.
Camera Press said in a short statement: "The Earl of Snowdon died peacefully at home on 13 January 2017."
Buckingham Palace said the Queen had been informed, but did not comment further.
He became famous for marrying – and later divorcing – the Queen's sister, Princess Margaret, who he met in the course of his photographic work.
Lord Snowdon began working as a photographer after he failed his second year exams at Jesus College, Cambridge.
He first worked as an apprentice under Royal photographer Baron, and later made his own way in the business, photographing actors including Laurence Olivier and Marlene Dietrich for theatre publicity shots.
His distinctive style of society photography helped him meet Princess Margaret – and hide his friendship with her. It worked as a cover, allowing him to slip in and out of Royal residences without arousing suspicion.
He became the first real commoner to wed a king's daughter for 450 years.
Antony Armstrong-Jones was the son of barrister Ronald Armstrong-Jones QC and society beauty Anne Messel, who went on to become the Countess of Rosse.
His parents separated when he was young and at 16 he contracted a form of polio, called poliomyelitis.
He overcame his disability by making a study of leg muscles and then devising exercises. The experience made him a life-long campaigner against the discrimination of disabled people.
He recovered well enough to be able to cox the Cambridge University rowing crew to victory in the 1950 Boat Race.
Following education at Sandroyd School, Salisbury, and then Eton, the young Armstrong-Jones went to Jesus College, Cambridge, to study natural history, but switched to architecture after only 10 days.
He later moved into photography, working from a Pimlico studio and a small house in unfashionable Rotherhithe on the banks of the Thames.
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But he was far from obscure. He held a one-man exhibition in 1956, and published two books the following year.
Over the years, he photographed many famous faces, from Baroness Thatcher, Dame Maggie Smith, Rupert Murdoch and Diana, Princess of Wales, to actors Jack Nicholson, Dame Joan Collins and Clint Eastwood.
The public stage, which was to bring glamour and marital disaster, was fully his on 26 February 1960, when his engagement to Princess Margaret was announced.
Five years earlier Margaret had ended her ill-fated relationship with divorced Group Captain Peter Townsend, choosing royal duty over love.
The wedding, on 6 May, was an impressive occasion at Westminster Abbey, after which the couple sailed around the Caribbean on their honeymoon.
The following year it was revealed that Princess Margaret was expecting a baby – the future Viscount Linley – and shortly afterwards the Queen brought Mr Armstrong-Jones fully into the royal fold by conferring an aristocratic title on him.
His title, the Earl of Snowdon, was chosen because of his family associations with Carnarvonshire, where his father was a deputy lord lieutenant.
In need of more stimulation that royal life could provide, he was appointed artistic adviser by The Sunday Times in 1962.
But his new professional position brought controversy. Questions were asked in the House of Commons over suggestions that his connections were bringing him special treatment.
The royal couple's second child, Lady Sarah Armstrong-Jones, was born on 1 May 1964.
Rumours of a rift in the marriage began as early as 1967, when foreign newspapers began to carry stories of a private "battle royal".
Lord Snowdon vigorously denied the reports, telling reporters: "I love my wife."
Then, in August 1970, an article appeared in the prestigious Ladies Home Journal in America, claiming there were severe problems in the marriage.
Buckingham Palace issued denials of reports that separation was being discussed by December of that year.
In January 1971, Lord Snowdon and Princess Margaret returned to the scene of their honeymoon in the Bahamas, and the fuss died down for a while.
Over the next five years the couple were seen together less and less, and almost all the press attention was directed to speculation about Lord Snowdon's "romances" with society ladies like Lady Jacqueline Rufus-Isaacs and Lady Harlech.
At the same time the popular press concluded a romance was on between Princess Margaret and landscape gardener Roddy Llewellyn, fuelled by their spending a holiday together in the Caribbean.
As the relationship became increasingly bitter, Lord Snowdon would reportedly make lists of "things I hate about you" and leave them in books Margaret was reading.
One note placed in her glove drawer allegedly read: "You look like a Jewish manicurist and I hate you."
By March 1976, the rift had gone too far to be mended, although many observers close to the Royal Family appeared to believe separation was unthinkable.
It was assumed the couple would simply lead separate lives without taking a formal decision.
But the split came on March 19 1976, with the Palace announcing they had "mutually agreed to live apart", adding that there were "no plans for divorce proceedings". They had been married for nearly 16 years.
Lord Snowdon was flying to Australia for an exhibition of his photographs when the news broke.
He made an almost tearful appearance in front of Australian television camera crews after he landed in Sydney, as he claimed he had not been warned of the announcement.
Lord Snowdon moved to a cottage in Sussex – and fresh speculation grew that his four-year friendship with film production assistant Lucy Lindsay-Hogg had triggered the official separation.
Divorce was announced on 11 May 1978, while Princess Margaret was in hospital suffering from gastroenteritis and hepatitis.
She became the first royal to divorce since Henry VIII.
The uncontested decree nisi was made in the High Court on 25 May 1978, and gossip columnists and writers settled into an account of the couple's lives as the "black sheep" of the Royal Family.
She, it was claimed, had lost interest in his arty friends, while he became bored by the constant rounds of royal pomp.
Princess Margaret had custody of the children; and divorce left Lord Snowdon free to wed Lucy Lindsay-Hogg in December 1978.
Despite the difficulties of their split, the pair remained friends in later years, becoming closer in the prolonged run up to Margaret's death in 2002.
Lord Snowdon had led an active royal life.
His first taste of public controversy came when he complained, with Everest climber Lord Hunt, about conditions at the Snowdon Hotel on the summit of Snowdon in North Wales.
As chairman of the panel of judges of souvenirs for the investiture of the Prince of Wales, he caused a storm by saying most of the 450 designs were a "load of rubbish".
In 1966 he had contributed to a design of a very different kind when he created the aviary at London Zoo.
Hints of a privately tempestuous nature came through a row with the freelance photographer Raymond Bellisario, who alleged that Lord Snowdon had complained about him to the Badminton Horse Trial authorities.
And in July 1971 stories of how he had thrown two glasses of wine over the Queen Mother's horse trainer Peter Cazalet began to appear.
But there was clearly "the joker" in him too. He admitted in 1974 that he had acted as a butler at a New York party, serving drinks, as a bet to see whether he would be recognised. He was not.
That year he made his maiden speech in the House of Lords, on the Sharp Report on the mobility of the disabled.
It led to his being invited to chair a parliamentary working party on the integration of disabled people, which reported in October 1976.
In January 1976 he had challenged the Royal Horticultural Society's organisation of the Chelsea Flower Show by writing a letter to The Times which angrily attacked their failure to allow blind people to take guide dogs into the annual show.
Then, the following year, he attacked the media and the Prime Minister James Callaghan for paying too little attention to the problems of the disabled.
His distance from the Royal Family was evident during the Silver Jubilee celebrations. He was given no official role, and sat eight rows behind Princess Margaret and his children at the Thanksgiving Service at St Paul's Cathedral.
Tragedy had struck privately. He narrowly missed death himself when racing driver Graham Hill and five team-mates were killed in a plane crash at Elstree. Lord Snowdon would also have been aboard but for a late change of plan.
And in 1983 he was temporarily blinded when an unidentified substance was squirted in his face by a group of four young men as he sat at traffic lights in a chauffeur-driven car.
Shortly after his divorce, he set up the Earl of Snowdon Award Scheme to provide bursaries for disabled students, using £14,000 from fees he received for photographs of the royal family.
In September 1980 he was appointed president for England of the International Year for Disabled People committee.
He attacked a decision to bar disabled Falklands soldiers and sailors from the City of London 1983 victory parade, and criticised the Princess of Wales's father, Earl Spencer, for his failure to provide public wheelchair access at his Althorp home.
In 1988, he hit out at British Rail for the conditions in which the disabled were forced to travel.
At the second annual presentation of the Snowdon Award Scheme, Lord Snowdon attacked Butlin's holiday camps for refusing to allow guide dogs admission to their sites, and the Church of England for threatening to get rid of a 400-acre adventure playground for disabled children in the grounds of a rectory.
His major interest in the disabled was revealed when he unveiled a prototype design for a motor-driven platform enabling handicapped people to move around in ordinary chairs.
The Squirrel wheelchair, as it was called, eventually went into production in Birmingham in 1989.
Although the idea never really took off, in 1988 he helped pioneer a revolutionary new hearing device called The Link, which aimed to make a human voice audible to the hard-of-hearing over other sounds in a crowded environment and was intended to be cheaper than existing devices.
He went on to design aids for the blind as well, and he also continued with his photographic career.
In 1983 Snowdon received nominations for the National Business Calendars Award and the Kodak Colour Calendar Awards for a tasteful black-and-white calendar, entitled Kindness, featuring portraits of hospital workers.
He was the first to photograph the newest member of the Royal Family in October 1984 when he took pictures of the one-month-old second son of the Prince and Princess of Wales, Prince Harry.
As a photographer, Lord Snowdon was in great demand commercially and in 1985 he spearheaded a £500,000 autumn promotional campaign for London Weekend Television, taking black and white photographs of the company's stars which were then used in a sequence of silent advertisements.
Lord Snowdon sparked controversy when he conducted an interview with Design Council chairman Simon Hornby for Vogue magazine in 1987. It led to bitter arguments within the Design Council because, according to Mr Hornby, the article took his comments about the Design Council services out of context, presenting them as condemnatory.
Snowdon was later forced to resign as consultant to the Council, a position he had held for 26 years.
In 1987 he became the UK patron of Rotary International's worldwide campaign against polio.
On good terms with his ex-wife, he took the official photographs of her and their two children on the eve of her tour of China in 1987, and nursed her back to health as she recovered from a lung operation in 1985.
At the age of 59, Lord Snowdon underwent a successful abdominal operation at the King Edward VII Hospital for Officers in London.
And at an age when most men are thinking about retirement, he changed jobs, moving from his position as designer and photographer at The Sunday Times to its main rival The Sunday Telegraph.
Lord Snowdon was continually facing new challenges in his determination to gain equal rights for the disabled.
In 1993 he took on the voluntary position of chairman of the Arts Council's initiative to increase the employment of disabled people in the arts.
Two years later, he became the first honorary president of the charitable trust ADAPT – Access for Disabled People to Arts Premises Today.
On 8 October 1993, his son Viscount Linley married the Honourable Serena Stanhope, in front of the Queen and other members of the Royal Family at Westminster Abbey.
Seven months later, his daughter Lady Sarah Armstrong-Jones announced her engagement to her long-time boyfriend, artist Daniel Chatto.
Their marriage followed a year later and gave Snowdon his first grandchild in 1996.
Earlier, in 1994, Lord Snowdon had again courted controversy when he emerged as the key figure in a campaign to sack his parish vicar, who did not believe in God.
Despite walking with an increasingly pronounced limp, forcing him to use a stick, Lord Snowdon continued his career as a professional photographer.
In 1995, he produced photographs for a 56-page celebration of British theatre for an edition of Vanity Fair magazine. It entailed 85 sittings, often up to three a day, with the top actors in British theatre.
Also in 1995 he succeeded the Earl of Gowrie as Provost of the Royal College of Art in London.
In 1999, he accepted a seat in the reformed House of Lords, becoming one of 10 hereditaries to be given life peerages. There was concern at his decision, considering he had missed all debates in the previous two full sessions of Parliament.
His love affairs remained colourful throughout.
He met his second wife Lucy Lindsay-Hogg, fourteen years his junior, in 1974, and they worked together in Australia on a BBC series called The Explorers for six weeks during that year.
Throughout their romance, including publicity surrounding Lord Snowdon's separation, she remained discreet.
When he revealed they were to marry at Kensington Register Office, it was to the Press Association – not even his personal assistant knew in advance.
She became the Countess of Snowdon on marrying him on December 15, 1978.
In April of the following year it was revealed that she was expecting a baby, which was born prematurely in July, 1979, and named Lady Frances Armstrong-Jones.
There was sadness – and scandal – when, on New Year's Eve 1996 his long-term mistress, journalist Ann Hills, took her life with a drugs overdose.
And Lord Snowdon's private life hit the headlines again in 1998 when, at the age of 68, he had an affair with Country Life journalist Melanie Cable-Alexander, 35, who bore him a son, Jasper.
Lucy, Countess of Snowdon, left him just weeks before the birth and their marriage ended in the divorce court in September 2000.
It later also emerged that he fathered an illegitimate daughter just before marrying Princess Margaret.
According to biographer Anne de Courcy, Polly Fry was born in 1960, in the third week of the royal newlyweds' honeymoon. She was brought up as a daughter of Jeremy Fry, inventor and member of the Fry's chocolate family.
A DNA test in 2004 apparently proved Lord Snowdon's paternity, but at the time Lord Snowdon denied knowledge of any claims or of a DNA test.
There were also rumours throughout his life that Lord Snowdon was bisexual.
"I didn't fall in love with boys – but a few men have been in love with me," he once said.
Interior designer Nicky Haslam claimed he had a "very brief romance" with Lord Snowdon the year before his wedding to Princess Margaret, but Snowdon denied it.
He went on to have a five-year relationship with Marjorie Wallace, the founder of the mental health charity Sane, but this cooled in in June 2008 after she talked too freely of their romance to the newspapers. However they remained friends.
Lord Snowdon was frail in his later years, using a wheelchair or sticks because of a recurrence of his childhood polio.
Although his granddaughter was a bridesmaid, he was not invited to the Duke and Duchess of Cambridge's wedding in 2011, but he was unfazed, apparently remarking: "I haven't been invited. Surprised? No. Will I be watching it on TV? I shouldn't think so."
He retired from the House of Lords in March 2016.
Although he was always something of an outsider, it was to him that the Queen and other royals often turned to capture their personal milestones in pictures.
He was the trusted "black sheep" of the Royal Family, the celebrated photographer with a weakness for romantic liaisons, and a tireless campaigner on behalf of the disabled.