"They were always on and off," adds the source. "They were always seeing other people." Still, when reports surfaced in March that Phillippe, 36, was father of his ex-girlfriend Alexis Knapp's baby, due this month, Seyfried, 25, stuck by him.
But it's anything but acrimonious post-split, says the pal. "There's no bad blood. They're cool."
Phillippe's past loves include ex-wife (and mother to his kids Ava and Deacon) Reese Witherspoon and actress Abbie Cornish. Red Riding Hood star Seyfried split with British beau Dominic Cooper about a year ago, following a three-year relationship.