Partner pees because he’s a heavy sleeper in bed

I’ve been with my partner for two years, we have a bonus child each and a 5 month old. There’s been a few times since the death of his Nan earlier this year where I’ve noticed he wees the bed, I didn’t notice prior because since his grandmother died I’ve been living with him. He’s a very heavy sleeper (imagine the stares from me he got while having a newborn) and I don’t know if he thinks I’ve realised as we haven’t talked about it, I just change the sheets. But now my sons been sleeping in our bed (he’s one and a half) and I wouldn’t want him rolling in pee. Is there anything out there he can do? And how do I bring it up I don’t want to embarrass him.