For the past few years we've come to expect to see new photos of the royal children on their birthdays.

Princess Charlotte turned three today and we all thought a cute new photo of her would be issued to celebrate the occasion. On her birthday last year, the family released a photo of the little girl that was taken by her mum, Duchess of Cambridge Kate Middleton. We were also treated to a very cute portrait of Prince George last July when he turned four. However, the official Kensington Palace Twitter account instead shared an old photo of Charlotte from the day she started nursery school, rather than a new photo, to mark the day.

Wishing a happy third birthday to Princess Charlotte – thank you all for your lovely messages! pic.twitter.com/IpLwFXveHp

— Kensington Palace (@KensingtonRoyal) May 2, 2018

It's thought that Kate and William bucked what's become a tradition after the siblings made a high-profile appearance last Monday when they visited their new brother Prince Louis in hospital. The royal couple are fiercely protective over their kids, said royal expert Penny Junor, and are likely waiting to release a new photo of the George and Charlotte with Louis to avoid them becoming overexposed.

"William and Kate won't want to overexpose their children," she told Elle.

"They have never been entirely conventional so I imagine they might release a photo in their own time, and it might be one Kate takes herself.

"A photo to commemorate the new baby's birth is hardly excessive however, and I would say, for historical purposes, it is important for there to be one.

That's something to look forward to, at least!