yep, that's the prevailing internet theory. well, idk about prevailing but it's pretty popular. there's also some speculation that tyrion is actually aerys' bastard via joanna lannister (or whatever tywin's wife/the lannister three's mother's name was, idr atm) but there's not really any evidence for it, it's pretty much just wild mass guessing. and that's not a spoiler for future books btw (at least i don't remember anything being mentioned specifically which gave rise to that theory).