Potty trained dog started pottying on our bed

I am so distressed. I’ve had my dog for about two years now and it was a long year and a few months to get him not to have accidents when he is unattended. He has recently discovered that he can jump on to the bed and has peed twice and pooped twice in the bed. It’s like he knows it wrong to potty on the floor but not the bed. I feel like I’m starting all over again and I don’t know what to do as he only does it when he’s alone.

This morning I took him outside. He peed, I left the house for 10 mins and when I came back he had pooped in the bed. He typically would poop either morning or evening. So when he didn’t when he went out this morning I didn’t think it was a big deal. How do I show him this unacceptable behavior if he never does it when I’m around??

What do I do now??