Nearly every celebrity swapped their glamorous Met Gala gown [1] for a sexy afterparty dress [2] once the ceremony was over on Monday, but there was one star who actually switched up her look before the fete even began: Amal Clooney. The Met Gala cohost wore full-skirted trousers by Richard Quinn [3] when she first hit the red carpet with George Clooney [4], but immediately after, she changed into a red mosaic column gown by Tom Ford [5]. And according to Anna Wintour, she had a good reason for doing so.

When Anna dropped by The Late Show With Stephen Colbert [6] on Thursday night, the Vogue editor revealed that Amal's first outfit was made out of "tin foil so she was a little bit concerned it might rip during the evening." So what did Amal do? She casually changed in the gift shop of the Metropolitan Museum of Art. No big deal, right? Check out Anna's full interview above and find out what other Met Gala secrets she revealed.