When their god unjustly loved my characters brother more than him they had a falling out and after some very pointed arguments over a romantic rivalry at a later point my character killed his twin brother, for this, he was cast out by their god and marked with a sign of the fallen, making him a fallen Aasimar.

Kaidahn the Murderer doesn't miss his brother Abelard, but their mother Evelyn and their father Adamund do.