‘Dirty’ joke cost me ‘Harry Potter’

It was no laughing matter.

“Stranger Things” star Jamie Campbell Bower, who plays lord of the “upside-down” Vecna in the Netflix series, has come a long way since he bombed his audition for the hero role of the “Harry Potter” franchise — if only his penchant for naughty jokes hadn’t gotten the best of him.

The 33-year-old actor revealed the blunder while appearing on Josh Horowitz’s “Happy Sad Confused” podcast.

As Bower tells it, the young actor had a meeting with the film’s first director, Chris Columbus, for which he was asked to prepare a joke.

“I had just heard this joke about a fairy,” recalled Bower.

“Like, the reason why the fairy sits on top of the Christmas tree. And it’s a really, like, dirty joke, because it’s about the Christmas tree up somebody’s bottom.”

The “Twilight” franchise star continued to describe how awkward things got after the punchline flopped.

“And I told this joke in the audition, and there was again, this sort of air of silence after I said it. And I was like, ‘Well, f – – ked that up,’ ” joked Bower.

Even though he lost the title role to Daniel Radcliffe, Bower still managed to appear in the franchise as a young Gellert Grindelwald in “Harry Potter and the Deathly Hallows: Part 1” and again in the spinoff “Fantastic Beasts: The Crimes of Grindelwald.”

Apparently, he’d cleaned up his act by the time he landed his role as the dark wizard, according to his manager, Lindsay Simon, who vouched for his return to the Wizarding World.

“Simon said, ‘Well, Jamie [is] now, you know, properly working, and is not telling too many rude jokes anymore,” joked the actor.