Aatrox and Rhaast

With Aatrox getting some new voice lines, I'm hoping some of them will shed more light on his relation to Rhaast. Rhaast says they have history and keeps calling him “brother” but by that does he mean “actual sibling” or just “fellow Darkin”?

While we’re at it, I’d love some backstory on Aatrox’s name.

I know in Real Life it’s just “atrocity” with some letters mushed around but it would be interesting to know if it’s got any specific meaning in-universe. We know “Rhaast” means “obey." For a guy who’s so obscenely gleeful about mass slaughter, he’s got a pretty gloomy name. You can even hear him sighing when he tells Kayn what his name means. Are Darkin names always a buzzkill or is it just a him thing?

I'd love to hear if any of you guys have ideas about these two.