Justin Theroux on the cringeworthy way his last high school relationship ended (Exclusive)

High school to college relationships can be messy, even for Justin Theroux.

On Saturday, the 46-year-old actor dished to ET's Nischelle Turner in New York, at a roundtable discussion with the cast of The Spy Who Dumped Me, about his worst breakup ever -- and it wasn't his recent split from Jennifer Aniston. In the film, Theroux plays Mila Kunis' ex-boyfriend, who turns out to actually be a CIA agent.

The cast was asked about their worst breakup stories and Theroux, 46, had a doozy.

Back when he was about 17, he said he had a pretty clingy girlfriend.

"I had a girl in high school who did that extra crazy thing where she … like, I was going to college and she had to stay here and she was like, 'I miss you, I love you, why aren’t we together' and I was like, '[I'm] going to work and trying to get ready for college.'"

Kunis interjected, "I feel like that’s very sweet, I don’t understand the problem."

Oh, but there was a problem.

"It sounds very sweet, then I did the romantic thing of surprising her. I made the money for the summer to go to college and then I was like, I’ve got two weeks before I got to go, let’s go see what she’s up to, you know, like 'click click,' open the door," Theroux continued. "Her roommate was like, 'Oh my god, what’re you doing here?' and then I was like, 'Shhh' and I went into her room and someone was there."

That would be, his girlfriend, plus someone else.

"And then I realized, her roommate wasn’t doing the 'Oh my god, what’re you doing here?' she was actually like, 'Oh god, what’re you doing here?' I was totally misreading the situation."

Instead of a romantic surprise, he described a very different feeling upon opening that door and seeing what he saw.

"Like blood, blood, blood coming out of my ears," he said.

The Spy Who Dumped Me hits theaters August 3.


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