There are celebrity couples, and then there are capital-C Couples, pairs that somehow make Gwyneth Paltrow, global tours, and red-carpet restraint all coexist in one surprisingly low-key love story.

After a high-profile marriage and subsequent divorce from Fergie, Josh Duhamel sparked a low-key romance with now-wife Audra Mari. “Everyone told me that after you get married you feel different,” ...