I accidentally saw my friend fully naked and now he blocked me, what can I do?

It all happened so quickly, I wasn't aware that he is changing his clothes, I went in and he was standing fully naked then I said sorry and left.

After that he blocked me, stopped talking with me and stopped showing up or gathering with our friends when I'm there.

When he see me randomly he ignores me and doesn't even look at me.

What can I do in this situation? Because he's an old friend and I feel so bad about it.

I accidentally saw my friend fully naked and now he blocked me, what can I do?
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