Sons first day of 4-K.

My son is very shy and has never been around other kids. He’s 4, almost 5 and starts 4 year old kindergarten Tuesday for 3 hours a day. I know he’s going to be scared to death of being left alone. Does anyone have any tips on how to make it easier? Do they let the parents stay till they’re comfortable? I’m just bawling thinking about him being scared and not wanting to be there. I know after a while he will love it and love being around kids but I’m just so nervous for him.