The pair became romantically involved while they were filming movie-musical Mamma Mia! even though the British actor was already in a committed relationship with girlfriend of 12 years Joanna Carolan.
Seyfried admits the "overlap" was "messy" so they parted ways and she started dating someone else - until Cooper split from his girlfriend in Britain and flew to the U.S. film set of her movie Dear John to win her back.
She tells Britain's Glamour magazine, "We fooled around so much during the rehearsals for Mamma Mia! But it was messy because there was some overlap with his girlfriend who he'd been with for 12 years. I didn't know how he was going to deal with that, so we went our separate ways and I began dating someone else. Then Dominic flew over to Charleston (South Carolina) where I was filming Dear John, and made sure I never saw that guy again."