How is Dark Messiah connected to Heroes of Might and Magic?

I've played through the entire trilogy of Heroes of Might and Magic V and Dark Messiah of Might and Magic more than once. I've studied the plot inside and out and tried to understand it as best as I could. I've read a lot of information about all of this and realized that it's quite possible that things aren't as simple as they seem... Throughout the game, I had the feeling that Biara wasn't indifferent to Agrael. There are many reasons for this, but that's not what I'm talking about right now. I shared my thoughts with a friend, and we came to a conclusion, which may not be entirely correct – you can judge us or praise us: Xana is the daughter of Agrael and Biara. I want to carefully listen to the arguments for and against and understand whether I'm the only one who came to this conclusion or if there's someone else who has also thought about it... :o :o :o