I think Mia Farrow's son Ronan was really fathered by Frank Sinatra. If you look at a photograph of Mia Farrow's son Ronan you would see that his resemblance to Frank Sinatra is much closer than his resemblance to Woody Allen, who is the other possible father of Mia Farrow's son Ronan.
Ronan is too good-looking to be Woody Allen's son. I do think I detect some of Frank Sinatra's facial features in Ronan's appearance, as well. Based on Ronan's remarks about the issue of his sister's allegations of sexual abuse, it seems that he might have inherited Sinatra's quick temper, as well.
It does not seem likely to me that Frank Sinatra would be the father. I feel like anyone can make up this story and saying that Frank Sinatra is the father is the easy story to make up. I guess there is a chance that he could be the father, but it does not seem very probable.
Ronan's parentage has been in question for a long time. The problem is that Mia Farrow has been so promiscuous her whole life that predicting the parentage of any of her children without a direct DNA test would have doubts associated with it. Had she led a more conservative sex life, there would not be so many questions.