Mark Ruffalo's handsome grown-up son is his double in rare family photos from 23rd birthday tribute

While some celebrity parents are busy with graduation season and prom , Mark Ruffalo had a birthday to celebrate in his household.

This week, the Poor Things actor celebrated his eldest son Keen's 23rd birthday, and shared a touching tribute in his honor.

The Marvel star has three kids with his wife Sunrise Coigney , who he married in 2000 after meeting on the street in 1998 thanks to a mutual friend. In addition to Keen, they are doting parents to daughters Bella Noche, 19, and Odette Moon, 16.

For Keen's special day, Mark took to Instagram and shared a round of photos of the birthday boy through the years.

He started with a throwback photo of him as a child standing in a field of yellow wildflowers, followed by more heartwarming photos of the two — that showcase their true resemblance to each other — plus he also included sweet pics of Keen and who appears to be his girlfriend, Laura.

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"Happy Birthday, Keen. Love you so much and proud of all you have accomplished this year. Keep going," Mark endearingly wrote in his caption.

Fans were then quick to take to the comments section under the post and gush over the birthday tribute, and note that Keen is Mark's double, with one writing: "Wait, he cloned himself. Happy birthday!" as others followed suit with: "Excited to see what the next generation of Ruffalo can accomplish," and: "You look like brothers! Happy Birthday to your son," as well as: "Wishing him the happiest of birthdays!"

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Though Mark spends much of his time in Los Angeles for work, his family is largely based in New York, where they have homes in the city as well as in the Catskills; the family moved to Sullivan County around 2008, and Mark has spoken fondly of the area.

© Instagram

Keen has had brief cameos in some of his dad's movies, Begin Again in 2013 and in Thor: Ragnarok in 2017, however he has yet to officially follow in his dad's acting footsteps, and it's unclear where he went to college.

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© Instagram

He has however supported his dad, as have his sisters, on occasional red carpets, and most recently, he was by his side when he received his star of the Hollywood Walk of Fame this past February.

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© Getty

He posed for pictures with his wife and kids — save for Odette — and in his speech, thanked them with: "My kids, Bella and Keen and Odette, you taught me so much about being a parent, being a man, being an actor, and this is your star, my whole family, in ways that you won't understand for some time."