Only Slightly Dead

sparknotes version: garrosh has a natural orcish skin tone, born on draenor. thrall is green and born on azeroth. since it was grom who caused the green to happen and he made a one-way trip to azeroth, there is no way he could have gone back to draenor to make a baby (who was not exposed to fel), then come back to die on azeroth.

expanded version: if we use the lords of war short and the chronicle books as a canon reference point, golka (garrosh’s mother) dies in a battle against the ogres roughly 11 years before the dark portal opens. so even if golka gave birth to garrosh and then immediately fought (and was left to die) in the gorian wars, that still makes garrosh bare minimum 11 years older than thrall, who is born in year 1 adp (after dark portal). grom drinks the demon blood three years before the dark portal opens. so garrosh had enough time to both have a relationship with his father enough to feel any attachment to the name hellscream and also to fully comprehend the shame and betrayal of his father falling to fel.

the red pox pandemic and garadar is established in the same year as well. so garrosh spends a minimum of three years orphaned with a deadly illness in quarantine/a hospice village knowing his dad is cracked out on demon roids leading a genocide death cult that is literally tearing the planet apart. kargath later comes to the town looking for more warriors but deems them all—especially garrosh—better off dead. this is how the town is informed that the rest of the orcs are travelling to another world. and once the dark portal is sealed, shattering draenor in the process, all anybody in the town of garadar knows for two entire decades is that the world is destroyed and it’s basically all garrosh’s dad’s fault.

so then thrall shows up, a mid 20s something, and approaches a suicidally-depressed chronically ill dude pushing 40 and goes. “hey there champ. you know. your dad wasnt that bad, boy. in fact, he was a brother to me.” grom even refers to thrall in warcraft 3 as “little brother”.