"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."
The video -- the second collaboration for Timberlake and Samberg since their 2006 viral hit "D--k in a Box" -- showed the two leaving prison after serving five months. As they toss out their wrapped boxes, they realize they've forgotten Mother's Day. No, worries - they ended up coming up with a plan. "I'm a motherlover, you're a motherlover," they rap. "We should f--- each other's mothers?"
Said Biel, "I thought it was amazing. I mean, it was so wrong, it's right. Just so wrong, it had to be right."
Susan Sarandon and Patricia Clarkson had cameos in the video, which was shot over a 20-hour period last week (Clarkson played Timberlake's mom).
"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."
"Motherlover" wasn't the only sketch that had Biel cracking up. On the show, Timberlake also joked about his relationship with Britney Spears and later dressed up as a singing breast implant.
"He was incredible," Biel said of her beau. "He just killed it."