Found gf's best friend on a porn site and don't know what to do

I [M31] was watching porn earlier and scrolling through some videos when I found my gfs [F27] best friend on there. I watched a little bit of the video and it turned me on a bit (she is very attractive, but I couldn't bring myself to jerk off to the video as, well, she's a friend of mine so it's a bit awkward) but I decided on another video. When I had finished, I was thinking about it. My gfs best friend is a struggling actor so probably decided to shoot some porn for a paycheque. Now while it doesn't bother me in the slightest (she's a 27 year old woman, she can do whatever the hell she likes with her life) I know it will upset my gf as my gf is generally quite shy and naive (she was a virgin before we started dating when she was 24 and hadn't done anything, even kissing before that) and is/was quite sheltered sexually while her friend is a lot more outgoing about these kind of things. If my gf found out, I know it would upset her. So I want to be the one to tell her if she were to find out, but I would rather she didn't find out if you know what I mean. Also it isn't for me to tell (maybe her friend wants the world to know, maybe she doesn't, it's not my decision to make). I clicked on her name on the website and some of the videos are quite explicit (there's not just straight porn, but lesbian, threesomes, step sister, school girl etc). What should I do in this situation?