Is it ok for a friend to date your ex?

I don't think it'll be okay.. But for sure this happens for some people. I don't know how they handle this, or if they are cool with this, but for me, it won't be really a good thing, especially if a friend knows that I was the previous lover of my ex.. It just sucks to hear or to know that a friend of mine dated my ex. I think as much as possible friends must take precautions and be sensitive about this kind of issues.. I don't know, what do you think about this?