Did you spot the sweet hidden detail in Prince George’s birthday portrait?

But what does it mean?

Prince George is growing up quickly, now the eldest of three, with his younger brother, Prince Louis, born just two months ago.

Marking the prince’s fifth birthday on Sunday, the Duke and Duchess of Cambridge released an unbelievably sweet photo of the third in line to the throne.

‘The Duke and Duchess of Cambridge are very pleased to share a new photograph of Prince George to mark his fifth birthday,’ captioned the snap on Kensington Palace’s official Instagram account. ‘Thank you everyone for your lovely messages.’

But it wasn’t his stylish blue look or rare grin that got the world talking after its release. Instead, it was a hidden detail, that proved that despite being a future King, Prince George is just a normal five-year-old.

While on first look, George’s outfit looks immaculate, on closer inspection, the bottom button on his shirt has been left undone.

It is not known whether leaving the button undone was a conscious decision or not, but either way, the message shone through. Prince George is a five-year-old boy first and foremost.

It is thought that George spent his birthday on holiday with his family on the Caribbean island of Mustique, with the Cambridges spotted boarding a private plane at St Lucia airport.

Happy birthday Prince George, and happy holiday to the Cambridges!