Princess Madeleine marked the day by sharing a ridiculously sweet set of photos on Facebook.
"Happy Birthday Sweet Leonore! You make us smile every day," the mum-of-two penned alongside a snap of the birthday girl holding up colourful balloons.
Leonore, who is Princess Madeleine and husband Chris O'Neill's eldest child, is big sister to her baby brother Prince Nicolas.
The Swedish royal palace also got in on the exciting occasion, showing a darling photo of the birthday girl wearing a very pretty pink dress and with a matching bow in her hair.
Fans from Sweden and across the globe shared their well-wishers for the little one.
One Facebook fan gushed, "Happy Birthday to beautiful sweet little Princess Leonore! Wishing you and your parents and little brother all the best!"
Another couldn't believe how fast her third birthday had come around, musing, "3! I can't believe it, she's getting so big! Happy Birthday to you, sweet Princess!"
She may look like a little cherub, but don't be fooled by Princess Leonore and her adorably cute cheeks.
The little royal's mum, Princess Madeleine recently shared what it was like encouraging her to read.
"Previously Leonore had not really had the patience," the 34-year-old admitted to Swedish news outlet Expressen. "But now we read more and more books, which is great fun!"
The royal's youngest is the polar opposite to his big sister.
"He has always loved books! So when you cannot find him, then he's sitting with a little book himself, up and down, like he was trying to look into it. It's very fun, so he will probably be a bookworm!"
And we think we know what book will be reigning supreme in Swedish royals' home.
The talented mum and royal is now adding a new title to her name - children's book author.
Madeleine, who has openly discussed that she suffers from dyslexia, is “working on a separate project, my book project."
The mum-of-two, who currently lives in London with her family, didn't tell the Swedish news outlet too much, simply revealing, “It’s a children’s book. You’ll see what is is soon. At the moment I can only say that it will be fun.”
The exciting new venture ties in with the Nordic beauty's work with the initiative "Room for Children" which promotes kids reading.
“Books are incredibly important. They open up your imagination and you learn a lot!"
We can only imagine the wonderful and magical tales the Swedish Princess has to share.
And who knows, maybe Madeleine will be reading to her fellow London-based royal cuties, Prince George and Princess Charlotte.
Last year she did admit that she'd love her two kids to have a play date with Kate and William's little ones.
"I would love [a playdate]. I'm sure we will cross paths – and who knows what we will do when we do!”