I might ask husband / father to check in, if that's necessary.
He could leave it vague, as in
Hey, your mom mentioned something about sheets today. Don't be embarrassed, I'm your dad and I'll talk fast, I promise.
Here's what happens sometimes. Don't worry, it won't happen forever, it's normal puberty stuff, everyone goes through it, even girls (except their bodies make it so it's not a mess to clean up).
On the other hand, son, if it's urine, we should get it checked out because it might be x, y, or z.
I'll leave it to you to tell me what's going on, okay? Remember, I'm here to help you. Nothing embarrasses me in any way. I'm a super ancient, old fart.