PHILADELPHIA -- Fifty years after Charles Xavier banded his first class of mutants together as the X-Men, the telepath-turned-team builder has been killed by one of them.

The teacher, who trained mutants in Marvel Entertainment's X-Men comics through the years, was felled in the latest issue of "Avengers vs. X-Men" by Scott Summers.

Summers, aka Cyclops, was one of the team's founding members. In the current series, he's been taken over by the Phoenix force and is lashing out.

Marvel editor in chief Axel Alonso says it wasn't writer Brian Michael Bendis' initial intent to kill the character off, but "as the story progressed it became obvious that this had to be the last stand of Charles Xavier."

He says the mortal blow will have ramifications that will reach into new titles coming this fall.