On "Saturday Night Live" this past weekend, host Justin Timberlake made a play for the affections of Susan Sarandon. His girlfriend, Jessica Biel, happened to be on set at the time, and when the raunchy skit got going, she was just as shocked as everyone else — and laughed just as hard.

Of course, the skit in question was the hilarious, risqué Digital Short "Motherlover," Timberlake and Andy Samberg's boundary-pushing follow-up to their viral sensation, "D--- in a Box," in which the duo hatch a plan to pay tribute to each other's single mommas by hooking up with them.

"I had an idea what it was going to be like, but I didn't see anything until the actual dress rehearsal where they have an audience and everything," Biel told MTV News while promoting her upcoming film, "Easy Virtue." "So, it was also a surprise to me."

What did she think of seeing her boyfriend singing such lines as, "I'm a motherlover, you're a motherlover/ We should f--- each other's mothers"? "I thought it was amazing," Biel said. "I mean, it was so wrong, it's right. Just so wrong, it had to be right."

She gave big props to Sarandon and Patricia Clarkson, who appeared as Justin's mother. "I was just so impressed that Susan and Patricia were a part of that," Biel said. "They are so amazing. First of all, they're so talented, incredible actresses, and they have such great sense of humors to say, 'Yeah, I want to be a part of that.' I was so impressed with them. They're so cool."

Biel also stepped in front of the cameras on Saturday night, introducing Ciara, who performed "Love Sex Magic" while Timberlake rocked the keyboard and provided backup vocals.

This wasn't the first time Biel had made an appearance on "SNL." In March, she sauntered onto the Weekend Update set dressed as cartoon heartbreaker Jessica Rabbit in a segment that also featured Samberg and Timberlake.

This past Saturday, though, Biel was content with a smaller role and the opportunity to watch her man in skits like the one in which he dressed up as a giant breast implant and rapped about the glories of plastic surgery.

"He was incredible," she said. "He just killed it."