"The days when a tabloid editor would say to his royal reporter `I want a royal splash for Monday and I don't care if it's true' are gone. O'Mara thinks readers are no longer satisfied by books based on what "a Palace source says" or "I understand from a close friend".The book also had a profound effect on the way the tabloid press reported the Royals "It totally altered the landscape," says Andrew Morton. "Royal biographies have to be more like political biographies when you are trying to give an honest picture of someone's political career."I get approached by dozens of people who have the inside story on something or other. But generally speaking they are of the Madame Vasso type and I don't think it's proper to publish that kind of material."The Diana book radically changed the style and content of royal bestsellers. "I think I've tried to set a new standard in royal publishing," he says.

He was the man behind Andrew Morton's Diana: Her True Story which in 1992 blew the whistle on Charles and Diana's marriage, hastening the announcement that they were to separate.The book was the stuff of publishers' dreams. In its first year, 4.5 million copies were sold world-wide, with translations in 23 languages. In O'Mara's office in Clapham, south London, the shelves are lined with different editions. Morton and O'Mara made millions from it.O'Mara, 52, says the secret of his success has been to do royal biographies seriously, with rigorous research and no idle speculation or tittle-tattle.