I wonder why people offer ethical opinions when all she wants is to know whether it's possible/likely. By the way, I'd say the odds are in you favour, but the human body may be unreliable. All the same, I wouldn't tell any of them until I found out, if finding out is possible while pregnant. The easiest way would be asking the other guy for a sample if you need it. Cos if you ask him for a sample to test and it's his, well there you go. If it is not his, he can forget all about it and move on. Just an opinion.