Peter Gallagher Reflects on Calling Chrismukkah 'Brilliant' Upon First Hearing It: ‘I Think That’s Gonna Stick’ (Exclusive).Linh

The term, created by Gallagher’s ‘The O.C.’ TV son Seth Cohen (Adam Brody), combines Christmas and Hanukkah

Peter Gallagher remembers the first time he heard the word “Chrismukkah,” long before it became an annual pop culture phenomenon.

On Wednesday, Oct. 23, PEOPLE spoke with The O.C. alum, 69, at the opening night of Broadway’s Left on Tenth — a play he stars in alongside Julianna Margulies.

While on the red carpet at the James Earl Jones Theatre in New York, Gallagher reflected on the holiday, first introduced by his TV son Adam Brody‘s character, Seth Cohen, on The O.C. in 2003. The hybrid name combines Christmas and Hanukkah and was created to celebrate the best that both holidays had to offer while bringing people with different backgrounds together.

“I just remember hearing Chrismukkah for the first time and thinking, ‘That’s brilliant. I think that’s gonna stick,’ and it did,” Gallagher, who starred as dad Sandy Cohen on the series, tells PEOPLE.

Rachel Bilson, known for her breakout role as Summer Roberts on the show, also recently spoke to PEOPLE about the holiday episode, adding that she plans to incorporate Chrismukkah into her real life as a mother.

THE O.C., Melinda Clarke, Mischa Barton, Peter Gallagher, Kelly Rowan, Adam Brody, 'The Chrismukkah Bar Mitz-vahkkah,' — THE O.C., Melinda Clarke, Mischa Barton, Peter Gallagher, Kelly Rowan, Adam Brody, “The Chrismukkah Bar Mitz-vahkkah”.WB/Everett

“I like teaching my daughter some of the Jewish traditions and things like that, but Chrismukkah itself is like its own holiday we haven’t really done,” Bilson, 43, told PEOPLE of her daughter Briar Rose, 9, whom she shares with ex Hayden Christensen. “But it sounds like this year might be the first.”

As for Gallagher — who has said in the past that he still keeps in touch with The O.C. cast — he couldn’t be more proud of his TV son.“I wouldn’t go as far as being a proud dad,” he tells PEOPLE while discussing the recent success of Brody’s Netflix series, Nobody Wants This.

“I haven’t seen the show, but I’m proud of him all the time as his friend and former TV dad, and I’m not surprised at all,” Gallagher says, calling Brody, 44, “so talented.”

“And I’m glad he’s still doing his thing.”

Gallagher’s latest role opposite Margulies, 58, for Left on Tenth is a romantic comedy by Delia Ephron based on her bestselling memoir of the same name.