New Lady Thatcher on the scene as Sir Mark weds

Sarah Russell is not a name that has frequently appeared in the headlines, but news that she is now officially Lady Thatcher is likely to change that for ever.

Yesterday, the son of the former prime minister Margaret Thatcher announced that he had married Ms Russell in Gibraltar last Thursday.

While Sir Mark Thatcher has been making headlines for decades, less is known about his wife. But the 42-year-old sister of Viscountess Rothermere, whose husband, Lord Rothermere, oversees the Daily Mail empire, is accustomed to moving in exalted circles.

In the 1980s she owned a string of restaurants, including Tiberio, a fashionable establishment near the Saudi Arabian embassy in Mayfair. The eldest daughter of the millionaire developer Terry Clemence, her first marriage – in 1996 – took her into the world of property and finance. She married Lord Francis Russell, an estate agent and chartered surveyor with a Knightsbridge office dealing in upmarket properties in central London. She abandoned her restaurant businesses and turned instead to decorating her new house, set in the 11,000-acre estate of Woburn Abbey.

But the Russells' relationship became acrimonious, not least because of the growing presence of Sir Mark in Sarah's life. The Russells were divorced in February last year. Sarah said that she began a relationship with Sir Mark only after she and her husband were living separate lives, but her former husband believed the affair began earlier. In 2006, after a row at her Clapham home, she called the police to persuade him to leave.

Sir Mark and Ms Russell were first alleged to have had an affair in 1989, long before her marriage to Lord Francis. A liaison was discovered after Sir Mark's former wife, Diane, hired a private detective in Dallas. Sir Mark and Sarah were photographed walking together in Paris.

They had met on holiday in the South of France in the summer of 1989. Ms Russell, who was with her parents and sisters, said her family were enjoying themselves while the Thatchers behaved like "Mr and Mrs Glum". At the time she said: "Mark is a friend of the family, that's all."

But by December 2006, after both their marriages had collapsed, Ms Russell was accepted into the Thatcher clan, even spending Christmas at the former prime minister's home in Belgravia.

Sir Mark and Diane were divorced in April last year after 18 years of marriage.

Sir Mark said that his mother was delighted at the news of his wedding: "I think that she could see, too, how things were going," he told The Sunday Telegraph. The couple plan to visit Baroness Thatcher after a honeymoon in the Middle East and the Indian Ocean.

News of the nuptials came days after Equatorial Guinea issued an arrest warrant over Sir Mark's alleged role in a failed 2004 coup. He allegedly provided money and transport for the uprising. Sir Mark denies direct involvement. He was given a fine and a suspended sentence in South Africa in 2005 after admitting unknowingly helping to finance the plot.