When Justin Timberlake's wedding guests say they can't talk about his lavish Italian nuptials, they're not being coy -- they mean they're legally forbidden from talking about it.

Jimmy Fallon, who watched his pal tie the knot with Jessica Biel in Southern Italy Oct. 19, told Andy Cohen during his Watch What Happens Live appearance Thursday, Nov. 1, that guests were required to sign a confidentiality agreement.

"I signed a contract," Fallon, 39, admitted to his host.

Though he couldn't spill any major details, the late night host said everyone was blown away by the beautiful bride, who opted for a pink Giambattista Valli gown for her trip down the aisle.

"She looked like a princess," Fallon gushed. And in general, "It was just insane. Everything was beautiful."

Even if Timberlake and Biel's big day been more understated, the comedian says he still would have had a blast.

"I'm a sucker for weddings," he shared. "I'm a fun person to invite to a wedding. Because I dance, I get up and drink. But then, I weep."