"I was working in New York so I literally was flying back on Halloween night. I had missed my flight. The whole crew of all our friends being the band members were waiting on me to get there and I was late," she said of her pals who dressed up as Timberlake's other *NSYNC band mates. "So my friends threw my outfit in the car. I went from the airport. I changed in the car."
Despite her late arrival -- and the fact that the initial idea was all Timberlake's -- Biel arguably made the costume by remembering that she and Timberlake had the actual jumpsuit he wore to the 1999 American Music Awards.
"I surprised Justin because I remembered that we have that exact jumpsuit that he wore in storage," she said. "So we pulled it out and it was the real one. It's for real. It's the real jumpsuit."
As for her husband's hair at the time, Biel quipped, "I'm probably not going to cut and perm [it]. I don't look as good."
To make Biel's look work as a couple's costume, Timberlake dressed up as a giant microphone.
"It was the hugest costume," she said of her husband's outfit. "It was so funny. He could barely move all night. It was this huge thing on his head. It was really fun, actually."
Biel and Timberlake's epic costumes came after the actress revealed that she wasn't the biggest fan of her now-husband's boy band back in the day. Watch the video below to hear what she had to say.