Is Ryan Phillippe's ex-girlfriend pregnant with his child?

Agostini/AP; King/FilmMagic

Ryan Phillippe, who dated Alexis Knapp last year, may be the father of her unborn baby.

Rumors of a hookup with Rihanna couldn't stop Ryan Phillippe and Amanda Seyfried's blossoming romance, but a baby might.

According to multiple reports, Phillippe's ex-girlfriend Alexis Knapp may be pregnant with his child.

The 26-year-old actress, who dated Phillippe last year following his split from Abbie Cornish, is in her second trimester, a source told UsMagazine.com.

Another source told the site Knapp "has been telling people" that Phillippe "is the father."

The insider admitted, however, that the actor "doesn't know if he is the dad."

"If he is, he will take full responsibility for the child," the source said.

People.com confirmed that "Alexis has told friends that the child is Ryan's" and added that she is due in June.

Phillippe, 36, is already father to 11-year-old Ava and 7-year-old Deacon, his children with ex-wife Reese Witherspoon.

After breaking up with Knapp in September, the "Lincoln Lawyer" star began dating Amanda Seyfried in late October.

It was reported in February that the couple had split among rumors that Phillippe was "secretly dating" Rihanna, but Seyfried herself denied it was true.

But if Phillippe did indeed father a child with Knapp, his romance with Seyfried might fizzle anyway.

And there are already signs of trouble in paradise.

The Daily News' Gatecrasher column reported on Monday that Seyfried left the "Lincoln Lawyer" premiere after-party on Thursday night looking "upset."

While a source told Gatecrasher that Seyfried seemed miffed Phillippe didn't want to leave with her, perhaps the issue was due to more than just a typical lovers' quarrel.

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