Liam posted a thirst trap pic of his chiseled bod with veins on his biceps so big they look like they might explode. And guess who liked the pic -- yep, Noah.

As you know, there's history here, folks. Miley dated/lived with Liam for years and married him in 2018. The marriage lasted less than 2 years and it was not a Paltrow kind of breakup, for sure. So Noah liking the post is, well, problematic.

There's more history here. As you may recall, Miley and Noah's mom, Tish, is now married to a dude Noah used to date -- Dominic Purcell. Noah dated Dominic for about 9 months, and when that relationship ended, Tish began seeing Dominic.

So yeah, it's messy.