Princess Diana used her honeymoon with Prince Charles to "catch up on sleep".

Princess Diana

Princess Diana

The late royal - who passed away in 1997 after she was involved in a fatal car crash in Paris aged 36 - was married to the 68-year-old Prince from 1981 until their divorce in 1996, and newly uncovered letters written by Diana state that she spent most of their romantic time away sleeping.

One letter, written to Diana's personal secretary Jane Parsons and dated August 15 1981, states: "The honeymoon was a perfect opportunity to catch up on sleep."

The newly discovered collection of letters, obtained by the Daily Telegraph newspaper, also include correspondence to Jane Parsons saying how pleased she was to see her son Prince William, who was one at the time, when she returned from her Royal tour of Australia in 1983.

She wrote: "William recognised us instantly, which was a relief as sometimes children resent their parents leaving them! It's marvellous to be home again and hopefully we won't have to do any more travelling this year... Wishful thinking!"

Princess Diana's letters will be sold at auction on April 12 at Stroud Auction Rooms in Gloucestershire, as part of the year-long celebrations of her life, in commemoration of the 20th anniversary of her death.

It's not the first time letters from the late royal have been uncovered either, as a letter written to her close friend and late interior designer Dudley Poplak in 1991, in which she described herself as feeling "extremely isolated", was released in January.

The letter read: "Dearest Dudley, I did so enjoy our lunch today - it was special for many reasons and in particular our conversation towards the end of our delicious meal.

"I do feel extremely isolated more than ever now, as I see what's coming to this country and this family.

"During the last couple of years I have been through a self-development programme which has brought a deep understanding of those who suffer and those who need love and support, wherever its in hospices or in the street.

"I feel that you believe in me, Dudley, and you've no idea what this means to me as I am continuously misunderstood by those around me.

"Please may we continue our conversation in January, when the pace of life isn't so fast and furious, as I'd care to ask for your advice and relay to you my inner thoughts.

"Lots of love from, Diana x."