While we've only witnessed one sighting of the royal cousins in public so far, courtesy of the Cambridge and Sussex family outing at the royal charity polo earlier this month, that of course doesn't mean they don't also spend plenty of time together in private too.
According to a source who spoke to Us Weekly, the Duke and Duchess of Cambridge's two eldest children, Prince George, who turns 6 today, and Princess Charlotte, 4, "dote" on their two-month-old cousin Archie.
"Charlotte treats Meghan and Harry's son like a little doll and is always asking after him," the insider tells the publication.
While Archie may not be old enough to run around with his older cousins, Prince George and Princess Charlotte apparently make an effort to include their younger brother, one-year-old Prince Louis, in as many of their activities as they can.
According to the source the Cambridge trio "have a blast together" and says, "Charlotte's a bit of a tomboy and loves climbing and sports.
"Although Charlotte's much bossier than George, she looks up to him.
"They squabble over small things like toys, but the majority of the time they get along."
While George and Charlotte didn't include their younger brother in their game of football during their outing to the polo, Louis seemed quite content to toddle around on his own (with Kate closely following behind) and at one point even cheekily teased his aunt and cousin.
In an adorable moment captured in a photograph, Prince Louis dons his mum's sunglasses and cheekily pokes out his tongue at Duchess Meghan and little Archie, much to Kate's amusement.
And according to another source that previously spoke to the same publication it was revealed that Archie had actually been present at Trooping the Colour in June this year too.
According to the source the young royal had accompanied his parents to the Queen's birthday celebration to "meet some of his cousins", but didn't join the family on the balcony.
"The reason Harry and Meghan didn't appear on the balcony when the Queen returned back to Buckingham Palace was because she was breastfeeding," the source told Us Weekly.
"She spent almost every moment with him and saying goodbye [before the parade] was very difficult.
"But Meghan truly wanted to be at the celebration for the queen."
With the summer break underway, the Cambridges are reportedly holidaying on the Caribbean island of Mustique, where Prince George will be celebrating his sixth birthday.
To mark the special occasion, Kensington Palace released three gorgeous images of the future King on Instagram, taken by the Duchess of Cambridge, who has often shared photographs of her children over the years.
The three images – two taken in the grounds of Kensington Palace and one while the family were on holiday – shows a relaxed and happy George, who sports an English football jersey in two of them and flashes a cheeky, toothy grin at the camera.
"🎈⚽️ Happy Birthday Prince George!," the Instagram caption begins.
"The Duke and Duchess of Cambridge are very pleased to share new photographs of Prince George to mark His Royal Highness's sixth birthday."
Adding: "Thank you everyone for all your lovely messages!"