Prince William feelings towards Prince Harry disclosed in unseen Princess Diana letters

In one of the letters, the Princess describes a special moment between her two children.

She wrote: "William adores his little brother and spends the entire time pouring an endless supply of hugs and kisses over Harry."

Collison, who Diana affectionately called Collie, remained close with the family until her death in 2013 at the age of 89.

The letters range from before her marriage to Charles, through to the early years of Prince William and Harry’s lives.

The correspondence is now being auctioned by Sworders in Stansted Mountfitchet in Essex.

Most of the letters to Collie are thank-you notes for birthday and Christmas presents given to Diana and her children, William and Harry.

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The latest latter features a Christmas and New Year from 1994.

A picture of Diana, William and Harry smiling is attached to the card.

Another double-sided letter written on Buckingham Palace notepaper is dated July 8, 1981 - three weeks before the Royal Wedding.

In it, Diana wrote "everyone frantically busy here doing last minute decorations… the bride to be has remained quite calm!".

This particular letter, which is in its original envelope addressed in Diana’s hand - is expected to sell for £800-1,200.

After the marriage of Diana’s parents ended, Collie followed Diana’s mother to London in 1967, working for her and her new husband until her retirement in 1973.

The collection of more than a dozen letters and cards is to be sold as part of the Out of the Ordinary Sale on July 30.