Here's the deal ... the Murder Inc honcho was N.O.R.E.'s latest guest on "Drink Champs," which just dropped. In preview clips of the episode, Irv could be heard recounting a lot of Ashanti stories -- including how he found out she had gotten involved with Nelly.

Unclear what year this was, but IG says he was watching an NBA game when he saw the two artists walk out and perform together -- which left him stunned at the time, as he himself was apparently romantically linked to her too around the same time. Sounds like he still has some sour grapes over it ... and about his complicated relationship with Ashanti in general.

More on that in a bit ... but first, fast-forward to Friday night -- where Nelly, Ja Rule, Ma$e, Ashanti, Lil Jon and others were headlining the "My 2000s Playlist" concert in Oakland.

Now, they were already on the bill, which was established well before the new "Drink Champs" episode -- but people still lost it on social media when they saw that Nelly actually brought out Ashanti during his set ... this after hers had concluded a few hours earlier.

Some are speculating this might've been a petty play at Irv's expense ... which may be true, especially when you hear Nelly's final joke about "floor seats" at the next NBA game.

Folks can make of this what they will, we suppose, but the timing of it is certainly not lost on people ... even though it may have just came together timing-wise by mere chance.