Handwritten letters and cards from Diana, Princess of Wales, to her family’s former housekeeper are to be sold at auction.

Violet Collison, who Diana affectionately called Collie, was head housekeeper to her parents at Park House on the Sandringham Estate in Norfolk where Diana spent her childhood years.

The correspondence, being auctioned by Sworders in Stansted Mountfitchet in Essex, reveals that Collie remained in Diana’s thoughts throughout her life.

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

These notes often include a line or two about Diana’s life at the time.

In one letter, written from Kensington Palace on September 25 1984, Diana thanked Collie for a gift to Harry.

She noted that “William adores his little brother & spends the entire time pouring an endless supply of hugs & kisses over Harry”.

A double-sided letter, written on Buckingham Palace notepaper, was 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!”.

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.

Collie died in 2013 at the age of 89.

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.

The items are expected to sell for thousands of pounds.