"Happy Birthday beautiful @selenagomez," Kerr wrote on Instagram.
VanderWaal appeared to attend a surprise party for Gomez in Los Angeles.
"huge HAPPY BIRTHDAY TODAY 4 SELENA!!!!!!!!!! Thank for everything I hope you have the best day bebegurllllllll," she captioned a photo of the "Wolves" singer.
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Swift and Gomez are close friends who collaborated on Swift's "Bad Blood" music video in 2015. Gomez's mom, Mandy Teefey, told Entertainment Tonight in May that Swift has "always been there" for Gomez.
"What I love about that friendship is it's so solid, and with Taylor, I feel like they can tell each other anything, and it will be an honest, in-your-best-interest kind of relationship," Teefey said. "It's not about anything else, and it's one you don't just find out here."
"They came up together, they just have never parted, so it's really a true friendship," she added.
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