Kate Middleton shared a new photo of Prince Louis for his third birthday and royal fans can't believe how much he's grown

Kate Middleton and Prince William shared a new photo of their son, Prince Louis, to mark his third birthday today.

• An official birthday photo, taken by Kate Middleton, has been shared to mark Prince Louis' third birthday today.
• Royal fans can't believe how much Prince Louis has grown and pointed out just how much he looks like his mum and siblings in the picture.
• This royal news comes after Kate Middleton was spotted shopping with Prince George and Princess Charlotte during their Easter break from school.

Three years ago today, Kate and William welcomed their third Cambridge child in the Lindo Wing of St Mary's Hospital in London.

Today little Prince Louis is celebrating his third birthday and Kate and William released an official birthday photo to mark the occasion.

The image, taken by the Duchess of Cambridge before Prince Louis' first day of nursery earlier this week, was shared on the Kensington Royal Instagram account.

The adorable photo shows the little prince grinning on a red balance bike, wearing a backpack with blue shorts, a navy jumper and a striped blue shirt underneath.

Royal fans flooded the comment section with birthday wishes and many were in disbelief by how much Prince Louis has grown and how quickly his third birthday has come around.

'Our baby is not a baby anymore😭 Happy birthday❤️,' one wrote.

'Wow he’s grown so much,' agreed another.

'Those 3 years have flown by! ❤️,' one more wrote, while a fourth added, 'Oh my! When did he become such a big boy.'

'He looks so cute, can’t believe he’s 3 years old already and looking like he’s a fully grown adult 😭 Happy Birthday Lou ❤️,' penned another royal supporter.

Others were fascinated by little Louis' resemblance to his mum, Kate Middleton, and siblings, Prince George and Princess Charlotte.

'He looks like his mum!! 😍,' one wrote, while a second chipped in, 'HE'S CLEARLY MUMMY TWIN!!!❤️'

'Funny - I thought he looked like his Brother and Daddy 😉😍,' a reply read.

Another pointed out his likeness to his brother, 'He’s just like George😱.'

One even saw a similarity to his grandfather, Michael Middleton - a comparison royal fans couldn't help but make when Prince Louis stepped out with the Cambridge family to attend a pantomime last December.

The Royal Family recently shared an unseen photograph of Prince Louis and six more of the Queen and Prince Philip's great-grandchildren spending time together at Balmoral.

In the gorgeous photo, baby Prince Louis can be seen sitting on the Queen's lap in a sitting room of Balmoral Castle.

'Captured by The Duchess of Cambridge 📷 The Queen and The Duke of Edinburgh surrounded by seven of their great-grandchildren at Balmoral Castle in 2018,' a caption beside the image read.

Prince Louis' birthday comes just days after the Queen's. Her Majesty turned 95 on Wednesday, facing her birthday as a widow.

She shared a poignant and personal message on the milestone day, thanking the public for their huge amount of support following the death of Prince Philip.

The official birthday release, signed from Elizabeth R, says, ‘I have, on the occasion of my 95th birthday today, received many messages of good wishes, which I very much appreciate.

‘While as a family we are in a period of great sadness, it has been a comfort to us all to see and hear the tributes paid to my husband, from those within the United Kingdom, the Commonwealth and around the world.

‘My family and I would like to thank you all for the support and kindess shown to us in recent days.

‘We have been deeply touched, and continue to be reminded that Philip had such an extraordinary impact on countless people throughout his life.’