Prince Charles and the Duchess of Cornwall have been damaged by Channel 4's documentary about Princess Diana, according to a royal biographer.

The Duchess and Prince Charles

The Duchess and Prince Charles

Sally Bedell Smith, who published 'Prince Charles: The Passions And Paradoxes Of An Improbable Life' earlier this year, has claimed that the controversial programme, entitled 'Diana: In Her Own Words', has brought their relationship back into the spotlight.

Of the show, which saw Diana speak candidly about her sex life with Prince Charles, she explained: "It's her voice that you are hearing again and in some cases for the first time."

However, Sally remains unsure as to whether the programme will do long-term damage to the royal couple, who tied the knot in 2005.

She told the Daily Express newspaper: "It's very difficult to tell. I think it will have caused some short-term damage, because it has stirred up memories of all that happened in the 1980s and 1990s all over again."

On the other hand, Joe Little of Majesty Magazine has rubbished the documentary, describing it as "muck-raking".

He said: "I think it made very uncomfortable viewing at times and also it struck me as slightly odd why she would have chosen to discuss such sensitive matters with her voice coach."

Joe also responded to suggestions that the programme has undermined Charles' hopes of making the Duchess the Queen in the future, saying he hopes that isn't the case.

But he added "it certainly isn't going to help their cause, because it puts them in a damaging light".