Can you guess what?
Prince George has been melting hearts since he arrived in 2013 – we can't believe he'll be seven this year! – along with his siblings Princess Charlotte, five, and Prince Louis, two.
Having started school a year and a half ago, George has this adorable nickhame from schoolfriends, although he and Charlotte are advised against having 'best friends'.
Earlier this year, the Duchess of Cambridge opened up about how 'terrifying' she found posing on the steps of the Lindo Wing for photographs after giving birth to her first child.
It's hard to imagine the oldest Cambridge child being called anything other than George now, but mum Kate reportedly 'had her heart set on' another boy's name while she was pregnant.
The couple chose not to find out the sex of their first child in advance, with Courtiers and friends of the couple insisting that they were leaving it as a surprise until the baby's arrival.
That said, Kate did have a favourite name in mind for a baby boy – although it wasn't George.
'Although Kate apparently suspected it was a boy and had set her heart on the name Alexander, they had not yet decided what to call their firstborn,' royal expert Katie Nicholl wrote in Vanity Fair.
'Kate was reported to have affectionately referred to her bump as ‘our little grape’ while she was pregnant, and there was a flurry of betting on possible names.'
Although the couple of course went with a different name for their firstborn, Alexander did make it as one of the prince's middle names – his full name being George Alexander Louis.
George is of course the name of the Queen's late father, King George VI.
We just can't imagine Prince George being an Alexander now – can you?