Prince Albert of Monaco is the father to four children.
But for years, his first-born daughter Jazmin Grace Grimaldi, 25, and his first-born son Alexandre Coste, 14, have lived the life of commoners.
While his twins with Charlene of Monaco, Prince Jacques and Princess Gabriella, two, have been raised royal.
Watch in the player above! Taking after her grandmother, Princess Grace of Monaco, Jazmin is a talented singer.
This is because Jazmin and Alexandre were born out of wedlock, and as Article 10 of the Constitution of Monaco dictates, they cannot be royal nor inherit the throne.
But that hasn't stopped the pair forming a loving bond and for the first time ever, we've been given a glimpse into just how close they are.
This week, proud big sister Jazmin shared a touching photo on Instagram with her little brother to mark his birthday.
Writing a message in French to her half-sibling, which translated to: "Happy birthday my brother!! fourteen years old!!!"
She capped off her post, which shows the pair smiling happily by the beach, with a slew of hashtags and emojis: "#officialteenager #joyeuxanniversaire #throwback #babybro #southoffrance #celebrate may all your birthday wishes come true."
Underneath the photo, Alex replied alongside two love heart emojis: "Thanks sis."
It appears the images are throwbacks and it's not known if Jazmin and Alex spent his actual birthday, which falls on August 24th, together.
Jazmin, whose mother Tamara Rotolo had a three week fling with the Prince during a holiday to the French Riviera in 1991, first rose to fame at the tender age of 14 when her father publicly acknowledged her as his daughter.
In 2015, she spoke to Harper's Bazaar about her unique situation.
"I was 14, getting ready to go to high school, when it hit the media that my father had a daughter, and it was me. It's a difficult time for any young adult, and it was an adjustment to have that attention. But I knew it was going to come someday," she reflected of the dramatic turn of events.
"I wanted that moment to connect with my father, to get to know him, and to have him get to know me," she said.
"Not having had that figure around, I missed that. It's wonderful that it happened when it did, and we've been enjoying a great relationship ever since."
Albert welcomed Alexandre in 2003 after a secret six-year relationship with flight attendant Nicole Coste.
His four children have never been pictured all together but aspiring singer Jazmin says she loves playing the doting big sister to the twins.
"I can't wait to be a sister to them and watch them grow up. They have these beautiful, big blue eyes – and they are both already so well behaved," she told Harper's of her half-siblings.