To royal fans around the world she was Princess Diana or 'the People's Princess', but to her family and her loved ones she was 'Duch'. Prince William and Prince Harry's mum went by the endearing nickname as a child and later on as an adult, a resurfaced Christmas card has revealed. Twitter user David Butler shared a photo of the card which showed Diana – by way of a change – signing off using her nickname and not her first name. "Wishing you a very Happy Christmas and New Year and lots of love from the four of us, Duch and Charles," the card read. Diana used the nickname in her personal life, among her sisters, but it's unusual to see her sign it on correspondence.

Her former chef Darren McGrady, author of Eating Royally, has revealed to HELLO! that Diana used to be called 'Duch' by her family because "when she was younger she always acted like a Duchess". He added: "I remember Sandringham one Christmas. She came into the kitchen with Sarah Ferguson and 'Fergie' called her 'Duch'. I was surprised because I knew she was a Princess and asked her why she had called her that." Of the Christmas card, Darren added: "I doubt very much this would have been sent to anyone other than a Spencer family member or perhaps The Yorks."

Diana signed the card 'Duch'

Like Diana, members of the royal family have different nicknames which they use for each other behind closed doors. Prince William always refers to his wife as 'Catherine' in public, but he calls her Kate in private. On the royal wedding official website prior to her becoming William's wife, it also stated: "Miss Middleton uses both names equally, and she has never expressed a preference for either Catherine or Kate since her engagement to Prince William. Catherine is the name that Miss Middleton grew up with in her family, and Kate is the name that she tends to use in a work context."

MORE: Cabbage, squeak, wombat - see the nicknames the royal family use

The couple have also been overheard calling each other 'darling' and 'babe' during engagements, and during the News of the World hacking trial, messages from William's phone revealed the Prince called his then-girlfriend 'baby' and 'babykins'.

See Princess Diana's sweetest moments with her boys:

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Meanwhile, William has previously revealed that his mother used to call him 'wombat'. In a 2007 interview with NBC's Matt Lauer, he explained: "It began when I was two. I've been rightfully told because I can't remember back that far. But when we went to Australia with our parents, and the wombat, you know, that's the local animal. So I just basically got called that. Not because I look like a wombat, or maybe I do."

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