I firmly believe that all fallen champion deaths are stupid.
In this case it was a Mist Elf that had just made his first homunculus and I was having fun letting it wreck everything by putting enemies to sleep. I had CLW so whenever it would get too injured I was heal it some. About 100 turns after I had made him I ended up at LN from N=. Hit by a bolt and I was dead.
Apparently healing companions turns you lawful VERY fast and I suppose I just had never been a neutral character with a heal spell and had a companion that I wanted to bother healing before. It's not super specific but I didn't even think about becoming too lawful.
Hopefully if this ever happens again I'll remember to kick some children after healing my companion, that'll keep me neutral in the grand scheme of things!
Edit : Oh yeah, he had far slayer and staff of the wanderer, so he was pretty set.