Years ago my dad accidentally did something similar in front of my wife.

My dad and step mom were going to host a dinner, and my wife was in the area a bit early and rather than go all the way home she texted them asking if she could just come over. My step mom told her it was no problem. My step mom did not mention, however, that she wasn't home and only my dad was there. In retrospect, my step mom should have gotten confirmation from my dad first.

So my wife goes over, knocks and loudly announces herself as she enters (they usually left their back door unlocked when home), and starts hanging out in the kitchen after no one answers her. This is fairly common in our family when gathering at their house.

Apparently my dad was showering and didn't hear my wife arrive. So he gets done with his shower and walks out of the bathroom fully naked, and goes right into the kitchen in full view of my wife. I'm told he was very startled and ran back into the bathroom.

They were both cool about it, as it was an honest mistake on everyone's part. It at least gave us a funny story for future family gatherings.