The new couple attempted to keep a low profile when they arrived separately to Hollywood hot spot 1Oak nightclub on Sunday night for Rihanna's after-party, but were later spotted leaving in the same chauffeured vehicle. Other guests at the event included French Montana, James Harden and Scott Disick.
Gomez, 24, appeared to be enjoying herself at the bash, and posted several videos to her Instagram story of the karaoke taking place at the party.
An eyewitness at the bash tells ET that Gomez and The Weeknd, whose real name is Abel Tesfaye, were super close and intimate throughout the night, and were even seen dancing together at one point in the evening. The party went on until 4 a.m., according to the eyewitness, and the two stayed until at least 2:45 a.m.
Another eyewitness tells ET that the two were quite cozy as they hung out at a VIP table with Montana and Harden, who both happen to be exes of Khloe Kardashian, as well as a few of The Weeknd's guy friends.
They also showed up to Republic Records' GRAMMY after-party at Catch LA earlier in the evening, and the 26-year-old singer -- who performed with Daft Punk at the awards show -- posed with music legend Stevie Wonder.
Meanwhile, Bieber was using Instagram's live feature to diss The Weeknd ...again. In a video captured by TMZ, the "Sorry" singer sarcastically told fans that his "favorite song of the moment" was "'Starboy' by The Weeknd." Bieber and his friends then erupt into laughter.
"Oh sh*t, that was funny," his friend exclaims off camera.
Bieber then quips, "We gotta end it now, y'all. Y'all, that was too funny."
This isn't the first time he's thrown shade at Gomez's new guy. A few weeks after the "Good for You" singer was spotted kissing Bella Hadid's ex-boyfriend, Bieber was asked by TMZ reporters if he would "listen to a Weeknd song" while outside Delilah, another celebrity hot spot in West Hollywood, California.
"Hell nah," he exclaimed. "That sh*t's whack!"
Additional reporting by Joseph Siyam and Jennifer Cady.