Royal fans can't believe how much Princess Charlotte looks like this royal - and, no, it's not the Queen!

It's already been a busy month of celebrations for the royal family, what with Prince Louis' first birthday, the Queen's 93rd, and the impending arrival of baby Sussex.

But today, it's all about Princess Charlotte, as the Duke and Duchess of Cambridge's only daughter celebrates her fourth birthday!

To mark the happy occasion, her parents last night unveiled three adorable portraits of the young royal, taken by the Duchess of Cambridge in the gardens of their Kensington Palace and Anmer Hall homes.

Royal fans were delighted to see new pictures of the Princess, hurrying in their droves to share comments and likes on the collection of photos.

Many fans also noted an uncanny resemblance between Charlotte - who hasn't been spotted in public since Princess Eugenie's wedding in October - and two other members of the royal family, dad Prince William and, of course, her grandmother Queen Elizabeth II.

One commented, 'She looks like William and Queen Elizabeth. Can’t believe she’s almost 4 💕💕'

While another follower agreed, saying, 'Mini William. Gorgeous', and a third wrote, 'She looks just like William 😍 how adorable!'

A fourth and fifth fan also said, 'Oh what a resemblance to Queen Elizabeth! 👑', and 'She looks so much like Queen Elizabeth!'

Looking back at photos of the Queen and Duke of Cambridge when they were around Charlotte's age, there's certainly a resemblance to be seen! What do you think?

It's likely that the Cambridge family are spending Charlotte's birthday as a family together at their Kensington Palace home - although the Princess may well be having part of her birthday at Willcocks Nursery, which she's been attending since last year.

Catherine, William and their children are likely all eagerly awaiting the birth of their new niece/nephew/cousin, with the Duchess of Sussex due to give birth to her baby with Prince Harry any day now!