Minutes into a Zoom interview with Henry Louis Gates Jr., he’s quoting Don King as he discusses two discoveries in season 12 of his PBS series Finding Your Roots: actress America Ferrera finding out one of her ancestors was a free mulatto of mixed African origin — and she’s a distant cousin of director Ava DuVernay — and actress Sanaa Lathan learning she’s the descendant of a wealthy white slave owner.

“Only in America,” says the host. “Or since America’s [family is] from Honduras, I should say, ‘Only in the Americas.’ ”

Since 2012, the Harvard professor has hosted the TV series in which he presents famous figures, from Tina Fey to Deepak Chopra, with a book of their families’ layered maternal and paternal histories, which come together via DNA testing and research gathered by genetic genealogy expert CeCe Moore and a team of three full-time genealogists. The conversations are at once revelatory, emotional and judgment-free. “There’s ‘stuff’ on every family tree,” says Gates.

As a host, you’re not just relaying personal information to guests; they’re opening up to you about their private family stories. How much time do you spend with them before filming?

I meet the guests on set. But there is one exception. If you were our guest and we found out that, let’s say, your daddy wasn’t your daddy but your daddy didn’t know, I have an ethics protocol and we would reach out to your publicist and say, “We’ve learned something in our research that we need to discuss directly.” And everybody knows it’s not good news. It’s like when your doctor calls you the same day you had a blood test. You go, “Oh shit, this is not going to say you’re going to live to 120.” So I would say, “We’ve discovered something in the course of our research that is forever going to change your understanding of your family. Do you want to know or not?” And then you would say, “Yes, of course, I want to know.” And I would say, “The man that you called your father is not your biological father.” Or, more likely, “The man you called your grandfather” — like in the case of Joe Manganiello — “had no biological relationship to you. Your grandmother had an affair” — in his case — “with a Black man.” In fact, Joe has done so much subsequent research that we’re thinking about doing a special segment in season 13, half of which features all the stuff that we’ve learned about him because the research goes on.