Where does the time go?
It's hard to believe that Prince Albert and Princess Charlene of Monaco's twins, Princess Gabriella and Prince Jacques, are officially four years old.
The adorable brother-sister duo rung in the exciting milestone moment on December 10th with a superhero-themed party fit for royalty.
Held on the grounds of the Palace of Monaco, Gabriella, Jacques and their VIP guests were treated to a visit from some very familiar faces, including Spider-Man and a surprise appearance from the Monaco's Fire Department's truck.
There to document every moment was proud mum and former Olympic swimmer, Princess Charlene, 40, who shared a sweet album from the day on her personal Instagram account.
It's a rare move for a royal to have their own social media page and while we'd never expect Duchess Catherine to post photos from her children's birthday parties, we love that Charlene is willing to share rare private moments with fans.
In one snap shared by South African-born Charlene, Gabriella, Jacques are treated to a ride in the fire truck's towering crane on the grounds of the palace.
In another photo, the twins dig in to a delicious-looking birthday cake with their friends.
"Such fun at our party! Thank you to our firemen for the surprise visit! Our true heroes," Princess Charlene penned alongside the birthday album.
For their second birthday, they threw a safari-themed bash and last year they embraced a museum theme complete with mechanical polar bears.
Opening up about their unbreakable bond, Charlene told French magazine "Point de Vue" earlier in the year: "We discover them even closer accomplices than we imagined."
As for Prince Albert, 60, whose mother was Hollywood actress turned royalty, Princess Grace of Monaco, he admits his dynamic duo are "very active, very playful, absolutely adorable, lots of fun and a lot of work."
Adding of their personalities: "Jacques is very reserved. He is sure of himself, but he likes to take his time doing things, to observe them, and no one can force him to do anything. Gabriella, for her part, is not afraid of anything. With her it is always full steam ahead!"
The twins were born in 2014 and although Princess Gabriella was born first, her younger brother will inherit the throne.
They also have two other half-siblings from Albert's previous relationships before he married Charlene.
Half-sister Jazmin Grace Grimaldi, 26, whose mother Tamara Rotolo had a three-week fling with the Prince during a holiday to the French Riviera in 1991, says she loves spending time with her younger brother and sister.
They also have half-brother Alexandre Coste, 15, who Albert welcomed in 2003 after a secret six-year relationship with flight attendant Nicole Coste.