Fortnite is destroying my 12yr old's sleep schedule

My kid has been obsessed with Fortnite for the last 6 months and I let him play on his Xbox after homework. Problem is he's staying up until 11pm some nights when we've got him on a 10pm bedtime. His grades are slipping and he's tired all the time. I'm thinking about taking the controller away but I don't want to be the bad guy. How do I enforce bedtime when gaming is involved?