Photos of John C. Reilly's son sends Twitter into frenzy: 'Biology is wild'

John C. Reilly is known to millions from his myriad acting credits, including cult hits like Talladega Nights and Step Brothers.

While he is a recognisable face, many will not be familiar with what his son Leo Reilly looks like - and they may be in for a surprise.

Leo has been forging a successful career for himself as a model, musician and TikTok star — he’s amassed over 700K followers on the platform — for years.

John C. Reilly attends Pasadena Playhouse presents Playhouse Celebrity Game Night: Speed Charades at Pasadena Playhouse on June 10, 2019 in Pasadena, California. (Photo by David Livingston/Getty Images)

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But he went insanely viral this week after HuffPost senior culture writer Zeba Bay tweeted out a photo of him and his famous father, noting, “so, the young man on the right is John C. Reilly’s son.”

Her comparison positively lit up on Twitter, racking up more than 14,000 likes and launching thousands of comments from apparently thirsty Twitter users.

Some simply could not even comprehend how the two were related.

“I need to see the mother,” one user wrote. “Her genes did what they had to do.”

“Wow, momma’s genes were up against a lot, but they persevered!” joked another.

“Thought this was an Internet Joke but after 20 seconds of research it turns out that loveleo is indeed John C Reilly’s son,” added another.

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Leo, 22, is the oldest son of John C. Reilly and his wife, film producer Alison Dickey — and yes, it seems he bears more resemblance to his mother than the Chicago actor.

According to IndieWire, the pair met while Dickey was working as Sean Penn’s assistant on the set of Casualties of War in 1989, which marked Reilly’s screen debut.

They have been married since 1992 and share two children together: Leo, who was born in 1998 and goes by “LoveLeo” on social media, and another son born three years later in 2001.

But as dashing as Leo may be, Twitter users fawning over the young star still seemingly wish to maintain that they mean no disrespect to his beloved father.

“I just want to clarify that I wasn’t trying to imply that John C. Reilly is ugly, just that biology is wild,” Blay said after her original tweet went viral.

“I’ve always had a lil crush on John tbh,” she added.

“just gonna say it. John C Reilly in his hat is a hot man,” wrote another user in defence of the Hollywood legend.

“makes sense bc everything John C. Reilly makes is great,” said a third.