Ariana Grande fans are coming around on her boyfriend Ethan Slater ... and all it took was an old clip of him showing off his muscles.

A ripped Ethan is shirtless in a resurfaced skit from a few years back, and now Ariana stans are giving her props for getting with her "Wicked" costar -- 'cause the dude looks good!

Ethan's been hiding a jacked physique on Broadway and during his public outings with Ariana ... until now, we haven't seen what his bod looks like. However, this old short film he was in from 2017 has been making the rounds anew, which features him wrestling his roommate over rent money. More importantly, we're getting a look at his bare torso ... and it's chiseled.

Abs, biceps, pecs ... you name it, Ethan's got it in this footage ... which had been innocuously floating around the internet until this week, when users on X posted it and tried to make it look like something it wasn't.

The real story here, though, is how Ariana fans are drooling over Ethan ... and starting to see what she sees in him.

Remember ... Ariana and Ethan got super close when they were filming "Wicked" together and they both divorced their spouses and got into a full-blown relationship. Safe to say ... the timeline seemed messy when it all came together.

As we've told you, Ariana and Ethan are spending almost all of their time together ... and they prefer spending it in private as opposed to gallivanting around town -- although, they do go out in public from time to time.

Now that we've seen more of Ethan's body ... it's no wonder Ariana wants him all to herself ... and that's kinda the consensus among her fans too. They're saying SpongeBob's a hunk!

For those who were on the fence before, the shirtless shots are pushing them over the edge.