At its heart, the long-running police drama “Blue Bloods” is really a show (a saga, if you like) about family. Fans may like to imagine that the casts of their favorite dramas, including “Blue Bloods,” are a kind of off-screen family as well as on, but it isn’t always the case. However, when a show runs as long as “Blue Bloods” has, some bonds between cast members are naturally going to grow and deepen over time. And according to a recent interview with “Blue Bloods” star Donnie Wahlberg, there’s just such a bond between himself and his onscreen dad, Tom Selleck.

Just how strong is this bond? It has affected no less than the names Wahlberg says he and Selleck address each other by, even when they’re not on camera. It might seem surprising at first, but according to Wahlberg, it couldn’t feel more natural for the two long-time professionals.

Their nicknames for each other reflect their relationship on the show

Wahlberg let slip that he and Selleck have a couple of somewhat unusual nicknames for each other even when they aren’t working on “Blue Bloods.” It all came out during an interview with “Entertainment Tonight” (posted on YouTube) in May of 2021 (via Outsider), during which he revealed the truth about his off-screen rapport with Selleck:

“I call him dad now, and he calls me son … I mean, that’s how we talk to each other off-camera. First he used to kind of grumble at me, like … ‘This music guy’s kind of weird.’ And then now he calls me son. And he’ll come in and give me a big hug. You know, you get a hug out of Tom Selleck, that’s a big deal.”

There you have it. If the next time you’re taking in an episode of “Blue Bloods” you’re struck by how convincing the father-son dynamic between Tom Selleck’s Frank Reagan and Donnie Wahlberg’s Danny Reagan is, remember that it feels that way to the actors playing these parts, too.