A TikTok user was watching Gossip Girl when she spotted Blake Lively making a funny clothing faux pas, and her video of the gaffe has already gone viral.

TikTok user skyehanamaikai noticed the mistake and recorded it.

The video has since received six million views.

Blake Lively (Serena) and Penn Badgley (Dan) co-star in a scene from the sixth season in which Lively is seen getting up from a restaurant table wearing a body-hugging coral dress. However, the camera pans over Lively when she makes a phone call a few seconds later, and she’s suddenly wearing a pair of cozy sweatpants beneath the dress.

She completes her ensemble with a Fendi snakeskin-print purse and a pair of Giuseppe Zanotti high heels.

In the video, TikTok user @skyehanamaikai says, “OK, I’m watching Gossip Girl, and here’s Serena standing up.”

“She looks great. There it is again. She looks good. But then…she’s wearing sweatpants,”  @skyehanamaikai says, laughing.

@skyehanamaikaiseason 6 episode 4 😗

♬ original sound – skyehanamaikai

Fans of “Gossip Girl” couldn’t believe they hadn’t spotted this earlier.

“I’ve watched gg 6 times already and never noticed,” one user said.

“The fact that I’ve rewatched gossip girl 3 times and still didn’t notice…” another added.

Blake believed she could get away with being a bit more comfortable behind the scenes because the sequence was meant to be shot from the waist up.

Let’s be honest: these days, we’re all on Zoom calls. On the top, it’s fancy, but on the bottom, it’s sweatpants. It’s got a whole 2020 vibe about it!

A TikTok user discovered a pair of contemporary water bottles make an unintentional appearance in a sequence from the Oscar-winning film “Little Women,” which is set in the 1800s, earlier this month. Whoops! The bottles are visible behind Timothée Chalamet, who plays Laurie in the movie.