Letters sent by Princess Diana have unveiled an insight into the relationship between Prince William and his brother Harry. The unseen communication between Diana and Violet Collison – the head housekeeper to her parents at Park House on the Sandringham Estate in Norfolk – is to be sold at auction. 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…