My relationship with my 'biological' dad is very complicated.
He never had a relationship with my mother, I was sort of like a love-child between them.
When I was three my dad moved away, but he kept in contact with my mum via email. When in 2008 I got my Facebook account and started talking to him myself over Facebook. After a little while I didn't get a response but I didn't mind because he travelled a lot to remote locations because he like to ski and play golf, he was very out doorsy.
Then on the 20th of March '11 I found out via Facebook that he died of cancer on Valentines Day which he had been fighting for 10 months which I also didn't know about.

I need help figuring out what to say to him, I wanted to send him a message on Facebook but I just don't know what to say. I want to say something about not knowing what to do, missing him and the fact that I didn't get to know him better, but I don't want to upset his wife because from talking to her I get the idea that she's doubtful about me being his child.

I'm a little confused about sending him a message on Facebook. If you have anything to say to him, write (or type) it out and then BURN it.

Yes, you're going to upset his wife (and probably his entire family) by posting such a message in a public place. Maybe people knew about you, maybe they didn't, but I think posting on Facebook is disrespectful to his memory.

If the wife wanted contact with you she would have notified you of his death. Didn't you and he ever discuss DNA testing and/or paternity?

In order to move on in the grieving process you very well may need to get your feelings out - posting on an open forum is not the way to do that.

(I am a widow; I know how the grieving process works.)

Did they have any children, down the road perhaps you may want to get to know them. But now is not the time to upset the, let them have their time to grieve also.

Write a journal if you want, tell him the things evey day that you would have wrote in face book, tell him about your life and what when on

I lost a very good friend about the same time from cancer and know that the battle takes it toll on the family and on the relationship often. Plus even if expected it is hard to deal with.

So write him in private for as long as it helps you in this.