This Friday, the most important movie of the year (it’s been empirically proven, don’t question it) hits theaters: Mamma Mia! Here We Go Again, the extremely sun-kissed sequel to 2008’s international smash Mamma Mia! As a member of a very stacked cast—Meryl Streep! Colin Firth! Christine Baranski! Andy Garcia! Cher!!—Dominic Cooper, playing the genial, abdominally blessed Sky, boyfriend to our charming lead Sophie (played by Amanda Seyfried), has a key role. At the beginning of the sequel, Sky, on a business trip in New York, and Sophie find themselves grappling with the challenges of a (temporarily) long-distance relationship. Will Sky find his way back to her? And, more pressingly, which ABBA hit will the two sing once he does?

The Mamma Mia! franchise has also influenced Cooper’s personal life. The 40-year-old actor—who can currently be seen in the third season of AMC’s Preacher as well—dated Seyfried in real life, after meeting her on the film, and the two were together for more than three years before splitting up. (Seyfried would tell Elle in 2011 that she “got her heart broken pretty hard.”) Seyfried is now married to actor Thomas Sadoski, and the two have a young child together—but Seyfried and Cooper still maintain a good relationship, even if she has said it was a bit awkward for Sadoski that she and her real-life ex-boyfriend were going to be reuniting on set.

We spoke to Cooper earlier this week to discuss the “high-school reunion” vibe of the sequel, how he felt about working with Seyfried, if he thinks there could potentially be a third Mamma Mia! film down the road, and Cher’s first impression of him.

Vanity Fair: At the screening I went to, the crowd was audibly cheering, clapping, and singing along for most of the film. What was it like for you seeing it for the first time?

Dominic Cooper: It was very exciting for me the other day. I saw it for the first time with the audience [at the premiere], and I kind of purposely made this decision—which was to wait until that audience on the premiere night, which was at the Hammersmith Apollo. So it’s a huge, huge amount of people. I’ve always had sort of slight amounts of anticipation as to whether people would respond so well to the slightly more emotional direction of this [sequel]. And they really did. It was a really sort of slow build. And it was clever putting together the story with flashbacks, the prequel into sequel. And I think [the audience] really went with it and took to it. It’s like this tiny ember that’s slightly getting brighter and brighter—and then by the end, when Cher steps on, it’s completely illuminating.

What was it like to reconvene with everyone, 10 years later?

I think it was unlike anything I could sort of quantify. Not that I’ve ever done this—I’ve always actually avoided this, and not been able to [go]—but it was like a school reunion. Your first thought is, Oh, what fun. Excellent. All these people! Then you think, Oh, my goodness, actually, 10 years. What have I done? What have I achieved? What have they done? What’s changed in their life? What’s changed in mine? Has anything changed, or has nothing changed? Will I be embarrassed? What do I look like now? You know? All this sudden paranoia that suddenly affect us, in the most ridiculous way. And what I then realized was actually how . . . what good friends we were and what good friends we’d become in that short space of time. And actually, we hadn’t had that great deal of contact [over the past decade], but we just sort of kicked off where we left off and it didn’t matter.

We all knew we’d experienced something extraordinary the first time around, and we all knew we were privileged enough to be experiencing it again. And I think in hindsight what we’ve learned, certainly what I’ve learned, was that I don’t know whether I took seriously enough the sort of impact that the film has had. . . . People have approached me and the rest of the cast and have said, “I really want to thank you because this film came at such an important time,” or “It was the last time I saw my mother, and we spent that time watching it together.” Or, “when someone in my family was ill, it really helped them through that struggle.” And I never ever saw it as being that [10 years ago]. That’s why I think when we all met again, we could celebrate that, because of how wonderfully people had received it without judgment and without mocking. I know Pierce [Brosnan] sustained abuse for his singing, but only as a sort of fun jibe. [Laughing] It was a particularly pleasant, lovely atmosphere [filming the sequel].

Is singing something you feel comfortable doing on-screen? How did your feelings about singing change in 10 years?

I think I beat it both times. It was part of my training; I’d done it. I just didn’t have confidence in it. . . . And I was terrified the first time I read the Mamma Mia script, and I actually didn’t really want to go to the audition, but I did, because I just thought I wouldn’t get it.

This time around, I really liked the song I had [“One of Us”]. This one complements the emotion of what’s happening, I think. And they’re still very hard songs to sing. What I found so rewarding and wonderful was my experience of being in a studio, one of the most famous studios in England, singing through a glass screen at the faces of [ABBA members] Benny [Andersson] and Björn [Ulvaeus]. You imagine them looking aghast and in horror at you devastating their songs, but they’re not. They’re unbelievably supportive. And this particular moment in time, I was struggling a bit with some of the song. Sometimes, in the studio environment, it’s a very dead environment: the sound is dead and you’re not getting any reverb and you’re just hearing your voice off a click track. And it wasn't helping me. And Benny just immediately dragged me out there and said, “Come sit down by the piano,” and he played it live with me. He built a temporary kind of board around my head, so I could be mic-ed. And I sang it live. Just an experience like that in itself, I will never forget—I’ll look back on it with such fondness.

Obviously, so much of Sky’s journey in both films relates directly to Sophie, and his relationship with her. How was your relationship working with Amanda, and how has it evolved over the 10 years?

It was very easy, lovely. I’ve been in contact with her. So it was like working with a friend. And I think working with a friend is always fun. They’re very honest with you. You’re not having to prove anything. It’s open, and it’s actually very, very, very easy. She’s so amenable, and nice to get on with and friendly to everyone on set and doesn’t come with any arrogance; yeah, she’s so easy to work with on set and to everyone around her. And she’s very kind to everyone. So, it’s an absolute joy, really. And everyone keeps saying, “Was it awkward and weird?” And it wasn’t. I’m sure there was a moment of trepidation about it, or thinking, What will it be like? But, there wasn’t any . . . Again, like with everyone else, it’s like being an old mate, or friends, that you just end up laughing with about the whole situation. She knows my family really well, and she’s good friends with them. She was in London, so she saw people that I knew, that we had met together. . . . She’s got a child and a lovely husband now. And they were there. It was all really, really great. It seems to be fine.

Did you get to interact with Cher at all on set? Any good anecdotes from being around her?

Yeah, she’s excellent. She took one look at me and didn’t trust me at all—and told me so herself, which I laughed out loud at.

She just said that right off the bat?

Yeah, kind of. After Amanda made it clear that we used to, once upon a time, be together, Cher said [to Seyfried], “You dodged a bullet there.”

That’s incredible.

Yeah, it’s very funny. She said it as a joke, but she thinks she knows me very well, the type of person I am. She’s so funny. She’s a really wonderful person to be around. I sat with her and her friend at dinner the other night, and we sort of joked about their path and how they met, these two best friends—[they were] both dating the same man at the same time or something, and then got rid of him and then had a good relationship for the last 40 years, which is much more important. . . . She was kind of just mesmerizing actually; there’s a reason she’s that popular. There’s a reason why everyone stands up and screams when she comes on-screen, because she’s someone who’s so good at doing that. She’s at her best when she’s performing. It was unlike anything I’d ever seen on a film set. When the lights went out in the studio and the spotlight came upon her and she started singing “Super Trouper,” it was just absolutely magical. We all watched in awe.

Do you think there’s a chance we would ever see a third movie or more in the franchise?

Well, what is exciting is . . . I’d spoke to Benny and Björn the other day—I love talking to them about their past and the history of the band. And they’ve got the band back together in the studio now recording. . . . So, who knows? They made such successful music, and they always said, “If we knew, we’d do it again, and again, and again.” And maybe them all being together again will do it. After this amount of time, after all the pressures of everything have gone . . . And if they do, then yes, there will be a third.

Are you aware of the photos from the first cast party that have gone around the Internet? It’s you dancing in Greece with Christine Baranski, and there’s I think one of Meryl, too. And you guys look like you’re having the most ecstatic time.

I think I have, yeah. I remember them.

Was that night as incredible as it looks from the photos?

Yeah, it was one of the best nights of my life. It was ABBA playing music in a bar in Greece. That’s why I’m just so lucky to have been part of something like this ever. This doesn’t happen. In the last 10 years I’ve gone, “My God, that was a really special, special time. And that happens so rarely.” And now, when you add Cher into the mix of that. I was chatting to Meryl [at the after-party] the other day, and then [she was] pulling Cher over, and I was talking about those two [about the movie], it’s ridiculous. It’s like a conversation I’m having down at the pub with my mates, but it’s not, it’s Meryl and Cher.

Lastly, I know you were recently at a polo match with Prince Harry and Meghan Markle. Did you get a chance to chat with them at all?

I’ve always gone to that polo match; I’ve known him from that match, and I know the girl that introduced Harry and Meghan. They couldn’t be more down to earth and lovely, those two. I love that America has gone completely mad for them. To me, they feel like people I’ve hung out with before. . . . They’re really gorgeous. I think they make a great couple. I’m excited. It’s really ignited America’s excitement for the royal family. I was in New Orleans when they got married. I walked past this rundown dilapidated bar at 7:00 in the morning, whatever time it was, and people in droves were going in there dressed to the nines in big, beautiful floral hats and wedding outfits. I was like, what on earth is happening? And then I realized they were dressed up to go to a bar, in New Orleans, to watch the royal wedding. To me, it seems ludicrous, but kind of wonderful.