The very first time William Solace died, he was stabbed.
At first, no one realized it. The others were all too caught up in their battles to notice the son of Apollo rushing to his surrounded boyfriend in efforts to help him, but never making it. No one realized that a monster went straight for him. No one noticed it throw him to the ground. No one saw it stab him through the heart and killing him instantly. No one realized until they found the body.
Frank found him first.