Here's the deal ... after PD's stunt this weekend -- in which his text messages to Ye surfaced, including a pic of him lying shirtless where he said he was "in bed with your wife" -- the late rapper started to trend on Twitter ... and the reason is because folks began to remember an old rumor about him, Ariana Grande and Pete from years ago.

You might recall ... Kanye himself actually invoked this unsubstantiated rumor a month ago when he was lashing out, writing "NO COMMENT" at the time. The rumor is that Pete allegedly sent Mac intimate photos of himself and Ari before Mac died -- and that, upon learning this and in the wake of Mac's death, AG broke things off with her then-fiancé.

Like we said, that rumor bubbled up online upon Pete and Ariana splitting -- and no media outlet reported it as true. Ariana's brother Frankie, also shot it down to our camera. And yet ... people felt that Pete doing something very similar here to Ye actually lent credence to the idea that maybe it happened.

Others felt it was a totally different situation, and more importantly ... completely inappropriate to bring up Mac with this new mess, with many calling on such talk to simmer down.

And yet, some couldn't help themselves with speculation -- arguing that if Pete was willing to do this with high-profile people like Kim and Kanye ... perhaps he could pull something similar with other love triangles he may have been involved in, including possibly Ari and Mac.