Princess Diana's upcoming Channel 4 documentary has been slammed as "deeply hurtful".

The late royal - who passed away in 1997 after being involved in a fatal car crash in Paris, France, aged 36 - is due to have private video recordings taken by her voice coach Peter Settelen aired on UK broadcaster Channel 4 next week as part of the documentary 'Diana: In Her Own Words'.

However, author Penny Junor - who has written studies on Diana's ex-husband Prince Charles and their sons Prince William and Prince Harry - has condemned the release of the tapes as "another way of exploiting" the late Princess.

According to the Daily Telegraph newspaper, Penny said: "This is just another way of exploiting Diana. It's not what Charles would want and it's clearly not what the boys would want. It will be deeply hurtful to them.

"It seems to me a very bad idea to broadcast these tapes, especially at this difficult time for the family."

The tapes - which were recorded during a series of meetings between Diana and Peter at Kensington Palace in 1992 and 1993 - were previously broadcast in the US in 2004 but have not been aired since, and in 2007 the BBC bought a portion of the footage, but scrapped the project after deeming it to be in bad taste.

Channel 4 deputy chief creative officer Ralph Lee, however, has said conversations could not be considered private because they were done in a question-and-answer style with a camera running, and therefore "there's nothing surreptitious" about the footage.

He said: "The idiom - that she's sitting on a sofa - is very familiar. She's very clearly talking to someone in front of a camera. There's nothing surreptitious.

"The word that has been used is that the footage is somehow 'ghoulish'. I simply don't agree with that. She is self-consciously and clearly taking part in a filmed process. I don't think viewers will feel greatly uneasy with that."

'Diana: In Her Own Words' will air in the UK on Channel 4 at 8pm on Sunday (06.08.17)