One possible issue that I would want considered is that he is shy and might reject that he has this interest and I definitely don't want to shame him.

I think that part is crucial to how you approach this. This mutual interest has been stigmatized in popular culture, like it or not, which could result in your brother feeling embarrassed and closing himself off to you in this context. That could create awkwardness for a long time.

Your goal is to open up on both sides and have someone close to you with whom you can talk about this openly.

Perhaps what you saw was him just checking it out and he does not have an interest. It is perfectly natural for people to get curious and look at things that they have no real interest in. It is called "educating oneself." Or this could be a genuine interest. You have no idea without asking, and asking is a risk.

It is easy to see that one piece of concrete evidence and let your brain start connecting dots that are not connected. Maybe he just likes foxes. People can like animals, real or not (e.g. dragons) without a sexual connection.

I recommend holding off and paying closer attention to clues in the future. You want to have someone to talk about this private topic with, but you do not want to close any doors, either. You need to be sure and not assume anything, else you risk damaging your relationship with your brother. Maybe broach the sexual topic first, without any fetishes. Maybe drop a comment (just one) about a sexual relationship you had, and see how he reacts. I never talked about this with my brother until we were adults, then we shared all sorts of interesting stories. But it took baby steps for us to open up: perhaps the same approach will work for you.