It's hardly a big deal. I've seen several of my friends naked in the locker room at the gym. In your case there's a surprise factor which will make it a little uncomfortable in that exact moment, but it's not something that will linger on unless you make it awkward yourself.
I have had a female friend change clothes in front of me and that was rather uncomfortable since we hardly knew each other back then, she is very attractive and I am uncomfortable in those kind of situations. The solution was simple. I looked away and I didn't talk about it and she didn't talk about it.
I have had a female friend change clothes in front of me and that was rather uncomfortable since we hardly knew each other back then, she is very attractive and I am uncomfortable in those kind of situations. The solution was simple. I looked away and I didn't talk about it and she didn't talk about it.