sons dad is in jail

Aubyrn • Freelance Artist//Mom to 2 boys
I just found out my 8 year olds biological father is in jail.
For what?, you may ask.
Driving a stolen vehicle and having meth on him.
Backstory: my son adores the shit out of the guy even though he has done very little for him but be in his life a little here and there. This is putting things nicely. His dad is also on monitored visitation. 
How do I tell him? He will be asking where his dad is, and while I'm against bad talking his dad ever, I'm against lying and he deserves to know a child friendly version of the truth.