The Imperius Curse!

Vera felt her jaw drop open, and she gaped at Sera, unaware that her grip on her friend had tightened even further.

“You -” She stammered, unable to even voice her disbelief. “You-what?” She managed to drop her gaze to her friend’s feet, tracking it back up and over Sera’s person as if she might be able to discern anything different. But of course there was something different, they hadn’t talked in years aside from the last time they’d seen each other. “H-how? For how long?”