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Lalo Villar, NBC
From left, Martin Sheen, translator Bautiman Lopez and Father Avellno, archivist at Tui Cathedral, in the upcoming episode of "Who Do You Think You Are?"

Word has traveled fast since NBC’s “Who Do You Think You Are?” started airing in 2010.

The show, which takes a variety of celebrities on a journey of family history, begins its third season on Feb. 3 at 7 p.m. and has become increasingly popular not just among viewers, but among celebrities.

Executive producer Lisa Kudrow said in a teleconference with TV critics that she gets approached all the time.

“I mean, I saw Blair Underwood (who will be featured in an episode this season) at a party and just walking by each other he said, ‘I want to do your show.’ And I said, ‘All right. Done.’”

“We’ve got a waiting list now,” she said.

The season premiere features Emmy Award-winning actor Martin Sheen. In the episode, Sheen, whose legal name is Ramon Estevez, explores his Spanish and Irish heritage. The actor gushed about the experience in a teleconference.

Sheen’s mother was from Ireland and his father from Spain. He was particularly curious about his ancestors’ involvement in social justice. He was pleased to find an uncle in each country heavily involved in their respective civil wars, fighting for what they believed in.

Sheen, not at all a stranger to protest and reform in his own life, suspects he must’ve gotten the trait from them.

“Not the extent that these gentlemen did because they were absolutely heroic and risked their lives,” he said. “But the message is clear that maybe this is part of my DNA.”

The episode follows Sheen on a journey to old prisons and a cathedral, partnering with historical and genealogical experts to unearth details about his ancestors’ lives, including an ironic revelation about his fourth removed grandfather, Don Diego Francisco Suarez, a Spanish judge. Sheen shared his findings with his family members, including his sister Carmen, who lives in Spain. The revelation about Don Diego “caused quite a bit of eyebrow raising,” he said.

And Sheen loved every minute of the process, right down to his family’s reactions.

“I wasn't always prepared for what I learned but the journey itself was deeply satisfying,” he said.

This season will feature 12 celebrities, making it the longest season so far (seasons 1 and 2 featured seven and eight celebrities, respectively). Besides Sheen, viewers will follow the genealogical journeys of Marisa Tomei, Blair Underwood, Helen Hunt, Reba McEntire, Jerome Bettis, Rita Wilson, Rob Lowe, Edie Falco, Rashida Jones and Jason Sudeikis.

One interviewer asked Kudrow if seasons will continue to grow like this.

“Well, I think a lot of people would love it to be a 20-episode season. So yes, expansion is good,” she said. “We always think more is better.”

She envisions a few other improvements over time.

“We would love to even get into more history — to get some context for what was going on,” she said. “I know in Helen Hunt's episode, I think that helped tremendously and ... we can see what was going on at the time and just how it motivated what they did."

In the meantime, the show has enjoyed a solid average of 6 million viewers, always ranking among the top three in its time slot each night. The whole franchise has seemingly taken global television by a storm. Kudrow first got the idea to produce an American version while watching the original U.K. version on BBC. There are now spin-off series in the U.S., Canada, Australia, Ireland, Denmark, Russia and South Africa, to name a few.

“I thought that this was such a fascinating show (the BBC version) and what a great way to deliver history on such a personal level,” Kudrow said. “You personalize it and it takes on a whole new meaning.”

In this third season, the U.S. spin-off continues partnership with Utah-based Ancestry.com.

The season premier shows Sheen beginning his search using the website.

He admitted that he’s not too tech-savvy. He doesn’t even own a computer, so he jumped at the opportunity to have the team of experts from “Who Do You Think You Are” research his family.

“I still intend to go online on the Ancestry.com,” he said, starting to chuckle, “because my wife knows how to do that."

Sheen and his wife, Janet, have been married 50 years. He said he is looking forward to continuing his family research with her help.