United Kingdom, May 10 -- Royal author Andrew Lownie has defended his allegation Sarah Ferguson had a secret and years-long "friends with benefits" relationship with disgraced rapper Sean 'Diddy' Combs.

The writer has spoken out after a source said to be close to the former Duchess of York, 66, dismissed the claim after it was printed by the Daily Mail as part of an extract from a new edition of Andrew's Entitled book on Sarah and her ex-husband Andrew Windsor.

Andrew told The Times about the claim: "I stand by it. It's fully sourced with former employees of P Diddy and Sarah Ferguson."

A portion of Entitled serialized in the Mail said Combs, 56, bragged to colleagues about sleeping with Ferguson.

He also allegedly once said "he could...