The stars of the superhero extravaganza known as “Suicide Squad’’ were joined on the red carpet at the movie’s glittering London premiere by Ben Affleck. The Cambridge-bred actor is barely in the movie, which arrives in theaters Friday, but he did star in another DC Comics franchise, “Batman v Superman: Dawn of Justice.’’ Affleck, looking tired but well-coiffed and wearing a gray suit and tie, posed for pics with fans. “Suicide Squad,’’ a big-budget action flick that the Globe’s Ty Burr describes as “a competent headache,’’ has a cast of thousands that includes Will Smith, Jared Leto, Margot Robbie, Joel Kinnaman, Viola Davis, Jai Courtney, Jay Hernandez, Adewale Akinnuoye-Agbaje, Ike Barinholtz, Scott Eastwood, and Cara Delevingne. Meanwhile, Ben’s wife (for now) Jennifer Garner was on “Today’’ and was asked about her relationship with her husband (for now). “We are definitely a modern family,’’ said Garner. “Ben was working in London on ‘Justice League’ and I felt like, ‘Well, the kids should have that experience.’ He and I are great friends and we just all went en masse. The kids and I had an amazing time, and he worked hard and got to join us for some. I want them to see everything’s OK.’’ Affleck and Garner announced a year ago that they plan to divorce, but there’s been speculation they’ve since reconciled.