Thank you for the summary of what he said. Unfortunately, he is incorrect about the Monegasque legal definition of (il)legitimacy - see the citations in my previous post.
To be fair, I don't think Alexandre was really suggesting a "legal" case under Monegasque law, just sharing his view of things.
I suppose that it *could* be an interesting angle for him to pursue, if he wants to be legitimized and recognized as the heir in the future. Based on this interview, he's a serious (and religious) young man who wants to maintain a sense of decorum relative to his father's office, who is studying business, and who is somewhat interested in working for his father in the future. (He mentions that his older maternal half-brothers work for their fathers, and he hasn't ruled out working with Albert.)
Albert is now 65, his heir apparent is only eight, and his wife/mother of heir has recurring problems of some kind that would seem to limit her ability to serve as regent. If Alexandre turns out to be as mature and capable as he seems in this interview, it's not impossible to imagine him as regent -- or even as heir, if Albert wanted to go in that direction.