Jennifer Lopez and Alex O'Loughlin star in a romantic comedy about a woman who conceives twins through artificial insemination, only to meet the man of her dreams on the very same day!

"It is a comedy that has romantic elements, it has a lot of physical comedy and it has a lot of dramatic moments, too," O'Loughlin tells ET at a party for his new CBS series, "Three Rivers."

"[Director] Alan Poul met with me and offered me the film," he continues. "I met Jennifer and it all seemed to fit. I went straight from the pilot of 'Three Rivers' to the movie, and I just finished the movie and started filming the show. It has been a non-stop ride the last few months. I think it is going to be a good film."

Lopez plays Zoe -- a woman who embarks on a journey to motherhood using artificial insemination, only to meet a possible Mr. Right named Stan (O'Loughlin) on the day of her insemination. The couple begins dating, with Zoe confusing their early relationship by hiding her pregnancy. After she reveals her secret, Stan unexpectedly sticks by her side. But as the birth approaches, the pressures of their new relationship and her impending motherhood could split them apart.

"Jennifer is amazing. I am very lucky," O'Loughlin says of his co-star.

"Three Rivers" will premiere Sunday, October 4 at 9 p.m. on CBS. 'The Back-Up Plan' will premiere in theaters in January 2010.