The actress/pop star went over to T-Swift's table at some point during the show -- a moment that was captured on a b-roll fan cam that was being broadcast from the Globes' own site ... showing behind-the-scenes stuff that didn't end up on TV.

Welp, eagle-eyed fans noticed this little meetup ... where SG rolls up on TayTay and a pal, Keleigh Teller, whispers something into Taylor's ear -- and then mouths something to her as well.

Keleigh, who's next to Taylor, appears to say "Timothée" and you see Selena nod emphatically.

While you can't hear much in the main clip circulating online, there's another video taken by a THR reporter who was standing nearby -- and who filmed part of this conversation. In their clip, you can hear Keleigh clearly say/ask "Timothée" ... just as many suspected.

Here's what the Internet thinks Selena said ... "I asked for a picture with him and she said no." Taylor looks shocked to hear this, and then the friend next to her asks if Selena means Timothée Chalamet ... and Selena confirms with the biggest, most exaggerated head gesture ever.

Of course, Kylie and Tim were in the building too ... and they were getting cozy throughout the show. It's unclear if/when Selena might've gone over there to chat -- but if what fans think they're seeing here is true ... it's interesting considering the interlinked history from all sides.

For starters, there's perceived bad blood between Selena and Kylie ... as well as with Hailey Bieber -- 'memba the whole "Mean Girls" eyebrows things? -- but they tried stamping that out.

When it comes to TC ... Selena shot a movie with the dude years ago, as love interests.

It'd only be natural for Selena to come on over and try to say hi to Timmy -- and a picture certainly wouldn't be out of the question either. You gotta wonder how exactly this may have gone down, and whether it was in Tim's presence or not ... assuming it happened at all.