I'm at a loss. Can you give me some advice?!

Samantha 🎣 • Mom of one bonus daughter👧 and 5 little boys 👶💙! 1 ceserian due to breech🔪. 4 VBACs💪 Married to my best friend.

I have a 4 and 1/2 year old boy that pees the bed, every single night. What stumps me is that he didn't use to. He just recently (the past month) started doing this. He was potty trained at 2 1/2 and quit having accidents COMPLETELY by 3. I don't know what to do? I have potty trained his 4 older siblings and never had this issue...? Please help.