Sir Elton John and David Furnish are proud parents to their two young sons, Zachary, 12, and Elijah, ten.
On Sunday, though, the singer announced that his family had expanded – and that his boys couldn't be happier.
Taking to his Instagram Stories, the star re-shared David's post, captioning it: "Happy Father's Day to us".
His husband's post showed an adorable picture of a tiny black labrador puppy. David sweetly captioned it: "This Father's Day, we are happy to announce the newest arrival to the Furnish-John family. Please meet Jacob [dog emoji, heart-eyes emoji].
"Zachary and Elijah are co-fathering little Jacob, and have proudly declared that Elton and I are… erm… grandparents…! Happy Father's Day to all the daddies and granddaddies out there [rocket emoji, red heart emoji] @eltonjohn."
Elizabeth Hurley's model son Damian was quick to react, commenting: "Can't wait until he gets to meet his Uncle Shivraj [heart emoji] xx," while actress Sharon Stone responded: "I'm in love," adding three heart-eyes emojis.
Other followers added: "Hello Jacob! You're a very lucky boy," "Gorgeous! Enjoy! And Happy Father's Day," and: "Happy Father's Day! Welcome Jacob, you are a cute and lucky guy".
Elton and David tend to keep their sons out of the public eye, only rarely sharing photos or insights into their family life. But a couple of months ago, David posted a snapshot of the two boys which showed how grown up they are and how unique their sense of style is.
Taking to Instagram, the 60-year-old shared several photos of his young sons at David Hockney's exhibition in London.
"An amazing afternoon introducing the boys to the extraordinary visual genius of #DavidHockney at @_lightroomldn," he wrote, before adding: "One of the things I love most about Hockney is his boundless curiosity and his embrace of new mediums and technology. @eltonjohn."
In the rare snaps, the brothers could be seen sitting on the floor, alongside other attendees, with their backs to the camera as they wore fashionable hoodies.
Whilst Elijah sported a £260 hoodie designed by Off-White, sibling Zachary is rocked a tie-dye Givenchy hoodie. The trio's outing in London came a week after David detailed their Easter holidays and expressed his pride at his kids' boarding skills.
"An awesome Easter Spring break holiday. Both boys finally gave snowboarding a try. Zachary preferred skis, but Elijah persevered and made amazing progress with his boarding skills. So proud of both of them," he wrote alongside a photo of them posing in the snow whilst kitted out in Moncler clothing.
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He added: "Many thanks to Dean and Tefi for coaching the boys so brilliantly, and Margaret at @alpineaspen for looking after the whole family. Big thanks also to @moncler for our cool kit."
When Elton turned 76 back in March, one of the sweetest aspects of his party was the sweet tribute his sons created for their famous dad.
The legendary singer took to Instagram to share some photos of the festivities and of them showed red and gold helium balloons arranged to spell out: "Happy Birthday Daddy 76". Elton gushed in the caption: "I absolutely loved my birthday! A magical day with @davidfurnish and our beautiful sons".