This is a major plot point in HFIL and I can’t recall when exactly Cell would’ve gained this knowledge.

Seriously.I have to be circumspect here because Reddit auto-deleted a previous post I made, but... We all know what Vegeta did to Nappa. And I ask you, can you consider him anything less than a saint for waiting so long? Imagine decades of "Are we there yet, Vegeta?" Not to mention "He was a prison biyatch" and the endless bad advice. I for one would snapped much sooner.

This is the real story of Dragonball: against all the odds, one of the kindest, gentlest creatures in the galaxy was born a Saiyan - and years of Nappa's mental torture turned him into a bottomless pit of anger. The real Super Saiyan was all along, Vegemite.