The TV presenter, 42, has become known for her boozy morning-after appearances on This Morning alongside her former co-host Phillip Schofield after pulling all-nighters at the annual event over the years.
However, the ITV star admitted she was forced into having an alcohol-free evening due to her tight-fitting dress, explaining how it restricted her from going to the bathroom.
After welcoming viewers to Wednesday’s This Morning, Willoughby’s co-host Craig Doyle made light of their lack of a hangover.
Reflecting on the night before, Doyle admitted: “I feel strong, and I don’t feel hungover,” with Willoughby quipping: “Well that’s a first.”
Willoughby then went on to explain why she looked so fresh-faced and how her strapless Suzanne Neville number was to blame.
She told viewers: “‘I loved my dress last night and I love getting dressed up and all glammed up, but the problem with that dress was, it was a bit wiggly and really tight around the thighs.
“So I had to go for a pee in the hotel, sorry for sharing so much right now but I am going to tell the truth, but I couldn’t pull it up to go for a pee and I was also tied in so tightly so nothing fell out of the top that I couldn’t pull it down .
“So, I had to go in the hotel and that was it until I knew I was getting home to the hotel,” she continued.
“It wasn’t until I was getting home from the O2, about five or six hours, [that I knew I couldn’t go again], so I only had about half a glass of prosecco.”
Poking fun at the anecdote, Doyle told Willoughby to “wait until you hit your 50s”, explaining she wouldn’t be able to go “10 minutes without needing a pee”.
Following the star-studded event, Willoughby revealed on Instagram how she chose to enjoy a McDonald’s instead of partying the night away.
Speaking to Lorraine in a preview clip ahead of This Morning, Willoughby said of her late-night snack: “I kept the pickles in as well, it felt like I needed a pickle at that point! It was incredible.”
While Doyle said of her late night fast food treat: “I was in a car with Alison and we were like, ‘No! Why didn’t she tell us?’”
This Morning airs weekdays from 10am on ITV1