Prince William became the Duke of Cambridge today just hours before he marries Kate Middleton in a historic ceremony watched by million across the globe.
The announcement means Miss Middleton will become Her Royal Highness the Duchess of Cambridge when the happy couple are pronounced husband and wife by the Archbishop of Canterbury.
The Queen marked the royal wedding by giving her grandson the dukedom - the highest rank in British peerage.
The news came as hundreds of thousands of well-wishers poured into London eager for a glimpse of the wedding.
Early morning trains, usually all-but deserted on a Bank Holiday, were packed with royal fans, some wearing mock tiaras, most clutching Union flags.
They were rewarded with the news that the happy couple will brave the elements and travel from Westminster Abbey to Buckingham Palace in the open-topped 1902 State Landau.
As the bride and groom awoke after spending the traditional night apart, thousands of well-wishers were already lining the processional route from Buckingham Palace to Westminster Abbey.
Forecasters' warnings of rain showers over central London failed to dampen the mounting excitement.
Paddy Harverson, the Prince of Wales's communications secretary, said William was relaxed and having breakfast ahead of his wedding.
The Dean of Westminster, Dr John Hall, who is officiating at the ceremony while the Archbishop of Canterbury marries the couple, predicted "a tremendously warm and uplifting day".
Months of meticulous preparations will come to fruition as the couple marry in front of 1,900 guests and a global television audience of two billion, just after 11am.
The world will get the first full view of the bride's dress when she steps out of the Rolls-Royce with her proud father Michael.
Miss Middleton, 29, will walk up the aisle on her father's arm as a commoner.
Just over an hour later she will return back down, with her new husband by her side, as a member of the Royal Family and a future Queen Catherine.
Tradition dictates that royal men receive a title on the morning of the wedding and it was up to the monarch to choose which one to bestow on her grandson and his new wife.
The last Duke of Cambridge, like Prince William, married a commoner for love. He wed the actress Sarah Louisa Fairbrother in 1847.
William also became the Earl of Strathearn and Baron Carrickfergus, which means Kate will become the Countess of Strathearn and Baroness Carrickfergus.
A host of politicians - including Prime Minister David Cameron - as well as clergy, military chiefs, ambassadors, more than 45 foreign royals and celebrity guests David and Victoria Beckham, Sir Elton John and Guy Ritchie will be guests inside the church.
There too will be William's proud grandparents the Queen and Duke of Edinburgh, his father the Prince of Wales and stepmother the Duchess of Cornwall, joined by some 40 members of the British royal family, as well as close friends and confidantes of the couple.
William, 28, and his brother Prince Harry, 26, who is his best man, will arrive at the historic 1,000-year-old church at 10.15am.
They both looked relaxed as they delighted waiting crowds in The Mall last night with an impromptu walkabout.
The groom, an RAF search and rescue helicopter pilot, will be dressed in red today, wearing the famous scarlet tunic of an Irish Guards officer rather than an Air Force uniform.
William faces a nailbiting 45-minute wait until his bride's arrival, part of which he will spend in private with Harry in the tiny side Chapel of St Edmund.
Kate spent her last night as a single woman with her parents, Michael and Carole, sister Pippa and brother James at the exclusive Goring hotel in Belgravia, just a stone's throw from Buckingham Palace.
The world will get the first glimpse of her dress, which has been kept a closely-guarded secret, when she leaves for the abbey exactly nine minutes before the service starts at 11am.
Hundreds of thousands of people are expected to line the mile-and-a-half route to Westminster Abbey, which takes in some of London's most famous landmarks as it passes through The Mall, Whitehall and Parliament Square.
Some 5,000 police officers are on duty as part of Britain's biggest security operation so far this century amid ongoing fears about the threat of terrorism and disruptive demonstrations.
The wedding service is a traditional religious affair with a strong flavour of "Britishness", and includes music by three of the nation's favourite composers, Elgar, Britten and Vaughan Williams.
The abbey has been decorated with an "avenue of trees" along the nave made up of eight English field maples and two hornbeams.
William and Kate's nuptials are the 15th to be celebrated at the holy site, which has witnessed 37 coronations over the centuries, beginning with William the Conqueror in 1066.
The wedding of this William comes more than a millennium after the first King William was crowned.
Kate is following in the footsteps of Diana, Princess of Wales, and will not promise to "obey" her new husband in her vows but instead to "love, comfort, honour and keep" him.
With William choosing not to wear a wedding ring, only he will say, "With this ring I thee wed," as he places the simple, slim band fashioned from a nugget of Welsh gold on his bride's finger.
The Archbishop of Canterbury, Dr Rowan Williams, is marrying the couple, the Bishop of London, the Rt Rev Richard Chartres, will give the address, and the Dean of Westminster, the Very Rev Dr John Hall, is conducting the service.
The witnesses who sign the historic marriage registers during the ceremony will be the Prince of Wales, the Duchess of Cornwall, Harry, Kate's parents, her sister Pippa and her brother James.
The guest list has provoked controversy, with the Foreign Office announcing the last-minute withdrawal of the Syrian ambassador's invitation yesterday in the wake of a bloody crackdown on protesters against president Bashar Assad.
Further questions have been raised about why former Labour prime ministers Tony Blair and Gordon Brown were not invited while Tory counterparts Sir John Major and Baroness Thatcher were.
After the ceremony William and Kate will ride back to Buckingham Palace in the open-top 1902 State Landau, the same fairytale horse-drawn carriage used by Charles and Diana on their wedding day 30 years earlier.
At 13.25, the bride and groom will step out onto the Palace's famous balcony, joined by the Queen and their families to watch the thundering flypast of a Lancaster, a Spitfire and a Hurricane from the Battle of Britain Memorial Flight and Two Tornado and Two Typhoon jets.
Then, the moment the world will be waiting for - the long-awaited kiss - the first time William and Kate have ever done so in public.
There will be two receptions at the palace, one with canapes hosted by the Queen in the afternoon for 650 guests, followed by the Prince of Wales's more intimate black-tie gathering of 300 close family and friends in the evening.
The 85-year-old monarch will skip the evening party, missing Harry's best man speech, by heading out of the capital with the Duke of Edinburgh for a private weekend, allowing guests to party the night away in her official London home.
The royal wedding is the culmination of a romance that began more than eight years ago when William and Kate met as students at St Andrews University in Fife, Scotland.
Their story has captured the hearts of people across the planet and thousands of foreign journalists, photographers and TV crews have descended on London to cover the event.
David Cameron, who will be in the abbey's quire with his wife Sam during the marriage service, told how he spent the night on the streets to get a good vantage point to watch William's parents, the Prince and Princess of Wales, marry in 1981.
Speaking to Sky News he said the marriage meant "quite a lot" to him personally.
He added: "I slept on the Mall for Charles and Diana's wedding all those years ago and I suppose like many people my age have watched Prince William grow up and all the challenges he's had - obviously losing his mother, but now finding love and wanting to get married.
"So like anyone who's lived in Britain, you feel quite an attachment to this whole event and that's why I think the whole country's getting excited about it."