I think the article mentioned that the son was concerned about his inheritance, but this is why your point about the pre-written pre-nup would have made more sense.

The son basically robbed his father of new love because of his jealousy and neuroses.

Hell, if I make it to 90, I hope I can still have an occassional romance.

The main thing I consider about Alzheimers affecting widows and widowers is that they now have the opportunity of a limited second chance without painful memories of the life and mobility they lost. Who knows what both elders were thinking when they were intimate? All we need to know is that they were in love. And getting laid.