While Taylor and other A-listers attending her party shared photos of the revelry via social media, Selena shared her feelings vocally, and it wasn't pretty.
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"She shouted, 'No one understands me! My boyfriend doesn't even understand me," an insider told Us Weekly, adding that bystanders -- "just stared [at her]."
Selena's meltdown about her on-again, off-again boyfriend of three years unfolded on the upper terrace of Taylor's New York apartment in the Tribeca area, where fellow partygoers noshed on pizza and sushi and drank beer.
The guest list for the "Blank Space" singer's birthday read like a who's who of entertainment: Justin Timberlake, Jay-Z and Beyonce, Sam Smith, Karlie Kloss, Nick Jonas and Olivia Culpo, Chrissy Teigen, 5 Seconds of Summer and others.
It appears that Taylor didn't let Selena's little tantrum get in the way of a good time, though, posting a photo on Instagram of the birthday shenanigans, saying, "So this is being 25…. #WHAT #bestbirthdayEVER."
In fairness, Selena did put on a happy face in another photo, standing next to her BFF as Taylor was presented with a birthday cake. Taylor Instagrammed the moment, captioning her photo, "When you're making a wish, but you already have all you really need standing around you."