My (F19) little brother (M16) came in my room while I was naked.

I need to preface this with some information first. I live in a 2 bedroom apartment with my boyfriend (M20) and my little brother (M16). I share one of the rooms with my boyfriend and my brother has the other one. It's a bit of a tight squeeze, but we make it work. <br><br>The issue is that our apartment doesn't have an elevator. For the past year, I've had chronic, debilitating pain in my legs and hips due to a health condition I have. Because of this, walking up the stairs to our apartment and going down to do laundry is extremely painful, so my brother helps with that. <br><br>In order to get to the laundry room, however, my brother has to go through my room since our front door is in our room and the door to the hallway is in the main area of our apartment. So, whenever he does laundry, he walks through my room. <br><br>This has never really posed as a problem for us, strangely enough. My brother knows to give me a yell before he comes through to warn me, and he doesn't even look at me. We've never had any problems with this. It's not ideal, but again, our living situation isn't either.<br><br>So, today, my boyfriend was out with some friends and I was getting ready to shower. I was walking out of my room with my towel and everything, and didn't realize my brother was going to do laundry. He came through and I was basically naked (I had a towel on) but he still saw me in the towel. <br><br>After he came through, he ran back into his room and closed the door. I think he was embarrassed. I don't know how to approach this. I want to apologize, but I don't know if it'll come off weird. What should I do?