Five ways Erik could have found out about Charles, but didn't…and the one way that he actually did.
One
He picks Alex as the most likely to recruit out of Charles' reduced team. The boy was already a rebel when they plucked him from prison, and Charles' rules had to chafe. Erik arranges to meet in a secluded park, "just to talk." Erik expects the anger and recriminations for his actions on the beach – he had just gone off and left them. What he's not prepared for is the photo of Charles that Alex hands him.
Erik studies it for a moment. Of course the wheelchair is a shock, but so are the dark circles under the eyes; the slightly sharper features; the hint of sadness underneath the posed smile. Erik says nothing. He pockets the photo and walks out.
Two
The first night that Emma is with him, Erik decides to test her powers by having her look in on Charles. Unlike Charles, there is no outward sign when she's using her telepathy; she just stares at the wall for a moment, and then she looks back at him with a cruel smile.
"Well, Magneto," she says, drawing out his name with a tone just shy of mockery, "you seem to have a talent for breaking telepaths."
Three
It's her first Christmas Eve since leaving Charles, and Raven's homesickness is overwhelming. Erik grudgingly gives her permission to visit the mansion. It's not that he's worried about Charles forcing her to stay; he knows the principled telepath too well to fear that. It's that he doubts her loyalty to him, to their cause. She's made such a drastic change in walking away from Charles; who's to say the mercurial Mystique won't change sides again? He sends Azazel with her, "because teleporting is the only way to get there tonight," he says, and as insurance against a sudden change of heart.
On Christmas morning, she greets Erik with a slap to the face and a "do you know what you did to him?"
Four
Erik ambushes Moira on the way home from her first day back at the CIA; snatching her car from a lonely spot on the road and depositing it in a dark culvert. She turns slightly dazed eyes to him when he climbs in beside her and demands to know what she told her bosses.
"He took most of my memories. I could honestly tell them that I don't know where he and the others are right now, or what they're doing. But I do remember one thing." She hesitates for a moment. Erik had nearly strangled her back on the beach – what would he do if he knew the effect of the bullet was permanet?
Then her eyes narrow. He deserves to know what his thirst for vengeance cost Charles. "The bullet left him paralyzed," she says bluntly. "He's going to be in a wheelchair for the rest of his life." Erik sits for a moment in stunned disbelief. He's tempted to call her a liar, but he doesn't need a telepath to read the truth in her face.
All of the little bits of metal in the car start rattling dangerously, and for a moment, Moira fears that she's signed her own death warrant. But the moment passes. Erik gets out of the car, and stalks off into the night. He leaves her stranded in the ditch.
Five
He walks into the crowded, noisy restaurant, expecting to meet the new recruit that Emma had identified. He leaves the helmet outside to avoid drawing unwanted attention. But the recruit is already there with someone else that Erik can only see from the back, a man sitting in a wheelchair. As Erik moves closer, he recognizes the cut of the dark, wavy hair, the shape of the neck, the familiar set of the shoulders, even the grey sportcoat. He stands there for a moment in silent disbelief. Then he turns and walks out the door.
He doesn't see Charles turn, surprised, eyes searching the crowd for him.
How He Got the News
He visits the mansion for an impromptu late-night game of chess. Charles is sitting at his desk, writing. He is startled to see his old friend, and his expression is wary. Erik tries to put him at ease by inviting him to the chess board. Charles pauses for a long time. Erik thinks it's the helmet that is standing between them.
Finally Charles sighs and pushes himself back from the desk. It's then that Erik realizes that the opulent leather desk chair has been replaced by an austere wheelchair. He doesn't miss that it's made entirely from plastic. Erik can't find any words to say.
Charles gives him a small shrug. "It's my legs that don't work; the rest of me is perfectly fine and quite capable of beating you. So, white or black?"
"Black," Erik says, feeling a little dazed. He takes the only seat at the board. He doesn't think he'll win tonight.