When the third season of “Black-ish” arrives, the Johnson family will expand.

Fresh from the Broadway smash “Hamilton,” Daveed Diggs will have a season 3 arc as Rainbow Johnson’s brother, Johan, Variety can exclusively reveal.

Bow (Tracee Ellis Ross) and Johan, whose mother is a very laid-back, hippie-ish soul, had very different childhoods than Dre, and that’s partly why Johan will be a frequent thorn in Dre’s side. Dre Johnson (Anthony Anderson) has always feared that his kids will grow up to be overly pampered, and it sounds like Johan is the personification of those fears.

“He’s sort of a hipster, entitled kid who gets on Dre’s nerves,” creator and showrunner Kenya Barris said. “He’s constantly on a search for the best conditioner for his hair. He’s probably gone to Penn or Wharton and could have gotten a great-paying job, but he’s trying to find himself. That attitude more than anything makes Dre want to strangle him.”

For Diggs, who won a Tony for playing Thomas Jefferson and the Marquis de Lafayette in “Hamilton,” there’s even a tiny link to French culture.

Johan “has been to Paris twice and he’s like, ‘You Americans!'” Barris said. Johan, as it happens, doesn’t like his butter to be too cold and complains about Americans’ mania for refrigeration. “He’s like, ‘This butter’s making my croissant crumble,’” according to Barris. “Dre is constantly snatching food from him.”

The upside for Johan, who will have a “substantial” recurring arc in the third season, is that the Johnson kids think he’s extremely cool — except for Diane (Marsai Martin). “She’s not buying that sh*t,” Barris said.

Though Barris didn’t give an exact timetable, Diggs’ character will turn up “early” in Season 3. It’s not the actor’s only high-profile new role, by the way. Diggs has also lined up roles in the upcoming film “Wonder” and the HBO sports mockumentary “Tour de Pharmacy.”

Barris said that most members of the “Black-ish” cast have seen “Hamilton,” and they are all fans of the hit musical. Barris saw the show twice, and both times, he was struck by how electrifying Diggs was in his dual roles of Lafayette and Jefferson.

“I was completely blown away by the whole show,” Barris said. “Everyone was great, but there was a certain charismatic nature to [Diggs] when he came out. I noticed each time — he was the guy where the audience kind of [perked] up and said, ‘Oh my God, this guy!’ And I had heard through some of the cast members and through some other people that ‘Black-ish’ was his favorite show. We had been looking for someone to bring on for [that] role, and I felt like he would be such a welcome addition to the family.”

Barris also noted that Deon Cole, a fan favorite who plays Charlie, one of Dre’s work colleagues, will be back for the third season as well. Season 3 of “Black-ish” goes into production next week and arrives on ABC Sept. 21.

Diggs is repped by WME and Brookside Artist Management.