Billie Eilish had another kind of ICE on her mind Grammys night ... 'cause she sent the rumor mill into overdrive with a massive ring sitting right on that engagement finger!

The star had fans fully convinced she’s ready to level up with boo Nat Wolff, with that sparkler doing all the talking as she hit Sunday night’s Grammys at L.A.’s Crypto.com Arena.

The ring was impossible to miss -- a serious rock -- and once you clocked it, there was no unseeing it.

If it is an engagement ring, it looks like Nat’s wasting no time, popping the question just over a year into their romance ... and we don't blame him!

It was a huge night all around for Billie -- she snagged Song of the Year and used her moment to speak out against federal immigration raids, declaring "no one is illegal on stolen land."