X-Men: Legacy (1991) #212

Sins of the Father, part 1 of 3.  

Professor X is trying to rebuild memories of his past using other people's minds.  

But the past is coming back to haunt him in another way, as a swathe of tragic deaths turns out to be linked by only one factor: Brian Xavier, the Professor's long-dead father.  

And solving the mystery means paying a visit to the Hellfire Club...