Is there a hot new couple in town?
“He had his arm around Hailey and stayed by her side all night,” a source tells PEOPLE, adding that the duo left the bash together at 1 a.m. holding hands.
Last month, Baldwin, 20, and Mendes, 19, fueled dating rumors when they were spotted at Universal Studios’ Halloween Horror Nights and enjoying dinner together a few days later.
A rep for Mendes did not immediately respond to request for comment.
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Jenner’s boyfriend Blake Griffin also partied alongside the Keeping Up with the Kardashians reality star but the couple kept their PDA to a minimum.
However, “Kourtney and Younes looked adorable together,” says the source. “They were holding hands and had their arms around each other.”