Sean Penn puffs a cigarette, hangs with Hunter Biden at Soho House in Malibu

From “Mystic River” to mystery meetings.

Sean Penn was spotted linking up with first son Hunter Biden at Soho House in Malibu, Calif., Wednesday.

The “I Am Sam” star was photographed with a cigarette in his mouth, wearing a plaid blue shirt, a pair of jeans and holding a tan jacket as he exited his vehicle.

Biden, meanwhile, kept a low profile in a black baseball cap, aviator sunglasses, a dark denim jacket and a pair of gray slacks.

The two men were seen chatting casually while posted outside the swanky members-only club.

We’re told Penn, 63, and Biden, 54, have been spending a lot of time together lately, as they’ve recently been spotted visiting each other’s homes.

The nature of their newfound friendship is unclear, and reps did not immediately return Page Six’s request for comment on whether they were hanging out as pals or to discuss business.

Penn and Biden are not such an unlikely duo, however, as the former has a knack for seemingly befriending controversial figures.

The “Carlito’s Way” star once secretly met, partied and interviewed murderous drug lord Joaquin Guzman Loera — also known as “El Chapo” — for an essay published in Rolling Stone magazine.

“While I was surfing the waves of Malibu at age 9, he was already working in the marijuana and poppy fields of the remote mountains of Sinaloa,” Penn wrote of the former cartel leader in 2016.

“Today he runs the biggest international drug cartel the world has ever known, exceeding even that of Pablo Escobar.”

Penn also appeared in the Netflix doc “The Day I Met El Chapo: The Kate Del Castillo Story” in 2017.

Biden — who has been indicted on nine charges for allegedly dodging more than $1 million in taxes while living a hard-partying, “extravagant” life — is reportedly working on a doc about himself.

The Los Angeles Times reported in January that Hollywood attorney Kevin Morris is backing the project, which aims to show President Joe Biden’s son “painting, selling his art, raising his son, and navigating everyday life as a sober adult with ongoing criminal investigations.”

Nearly three years ago, Hunter — who originally hails from Delaware — moved to Malibu to better help him with his artistic pursuits.

In July 2021, he moved into a $20,000-a-month rental with his wife, South African model and filmmaker Melissa Cohen, and their son, Beau Jr.

Hunter told Artnet News at the time that he woke up at 5 a.m. every day, made a cup of coffee and went to the garage, which had been converted to an art studio with a tabletop for painting.

The “Beautiful Things” author added in the interview with the publication, “I don’t paint from emotion or feeling, which I think are both very ephemeral.

“For me, painting is much more about kind of trying to bring forth what is, I think, the universal truth.”