Traditionally royal babies are given several names – Kate's husband is William Arthur Philip Louis – which are chosen in tribute to members of their families.
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Elizabeth is the most obvious choice for their little Princess. As well as being a lovely tribute to William's grandmother, the name would also be relevant to the Middletons. Both Kate and her mother Carole have Elizabeth as a second name, after the Duchess' great-grandmother.
The advantage of this is that the baby could also be called Lizzy, Liz or Libby for short. The sovereign was famously called Lilibet by her close family and friends.
Another safe bet is Diana in honour of the Duke's adored mother. William will be keen to "make sure she doesn't miss out on the excitement", which is how he explained his decision to give his wife her iconic sapphire.
Given that Baby Cambridge will one day occupy the throne, Alexandra, Victoria and Mary are also suitable options. Queen Mary was the grandmother of the current monarch and bequeathed her many of her most magnificent jewels.
Naming her after Alexandra of Denmark, who was the wife of Edward VII and daughter-in-law of Queen Victoria, would bode well.
Known as Alix in the family, she had a reputation for being dignified, charming and jolly. The royal was also an expert horsewoman, with a fondness for ice-skating and dancing. Apart from the reference to equestrian pursuits, it's a description that could so easily fit Kate herself.
Other possibilities are Anne or Alice in honour of Prince Philip's mother. Kate's sister Pippa will almost probably be asked to be a godmother so she might inspire Philippa or Charlotte, which is her second name. The girls' closeness to their mum is well known so Carole will probably feature somewhere on the list.
Whatever the new parents decide on, this time they will probably aim to keep it close to their chests, until the big reveal in July.
Watch: Prince William takes George to meet his sister
It's a little princess!