Reese Witherspoon, who went on Conan to promote Big Little Lies, declared herself Irish to the television host on Tuesday's episode.
The actress, who celebrated her birthday on March 22, was on the talk show to promote her HBO series, but the conversation turned to her ancestry.
“I called your producer on the way here in the car because I was very excited,” Reese told O'Brien. “I did one of those genetic testing things and I found out that I’m 63 percent Irish. I had no idea. I thought I was Scottish and Welsh. It turns out my parents were full of s**t, I guess. But now I’m Irish!”
Reese continues in jest, “It just makes so much sense. I’m a really good drinker. I love St. Patrick’s Day. Potatoes are delicious. I’m looking forward to meeting all my cousins...”
“No, no — you don’t want to meet those people,” interrupts Conan.
“You and I are probably related!” Reese tells the Irish host.
In her Irish accent, Reese says, “Now I get to say things like, 'It's in me genes! I love that Conan' O'Brien; he's such a nice fella.”
Conan then tells Reese he's in fact 99.8 percent Irish. “I think I’m more Irish than people living in Ireland,” he jokes. “I looked into it and I was like, ‘That means I’m inbred!’”