After McConaughey suggested he and Harrelson could be half brothers, the Cheers alum weighed in on the possibility.
"Well, I'll just say there is some veracity to that thought," Harrelson, 61, said on the April 18 episode of The Late Show With Stephen Colbert, "because we talked to Ma Mac, Matthew's legitimate mother, and she let us know one time—it's crazy, we were in Greece. We were watching the U.S. team win the World Cup, and I don't know, I mentioned something about regrets. And I said, ‘You know, it's odd that my father has no regrets.' And I've known Ma Mac a long time, and she goes, 'I knew your father.'"
As he explained, it was how McConaughey's mother Mary McCabe said it that caught his attention.
"It was the ellipses I found a little troubling or interesting. 'I knew your father,'" Harrelson said, going on to describe the pause as "filled with innuendo."
The Triangle of Sadness star also indicated the timing would make sense.
"The year of his [McConaughey's] birth, nine months before," he said, "she was on a sabbatical from her relationship with his supposed father Jim."
And Harrelson noted the actors want to further explore whether they're related.
"The thing is we want to go and test," he shared. "But for him, it's a much more big deal. I mean, he feels like he's losing a father. But I'm like, no you're gaining a different father and a brother."
McConaughey—who appeared alongside Harrelson in the show True Detective—first brought up the potential family ties last week.
"In Greece a few years ago, we're sitting around talking about how close we are and our families and etcetera and my mom is there. And she says, ‘Woody, I knew your dad,'" the Oscar winner, 53, said on the April 12 episode of Kelly Ripa's podcast Let's Talk Off Camera. "Everyone was aware of the ellipses that my mom left after 'knew.' It was a loaded K-N-E-W."
And he also noted the timeline would add up.
"We went on to unpack this what 'knew' meant and did some math and found out that his dad was on furlough at the same time that my mom and dad were in their second divorce," McConaughey added. "Then there's possible receipts and places out in West Texas where there might have been a gathering, or a meeting or a 'knew' moment."
If the duo were to be half brothers, they wouldn't be the only stars with famous family members. To see more celebrities you may not have known are related, keep scrolling.