Who is his father?

I just recently saw the end half of the movie "Shot in the Dark". I saw where he was talking to the 2 men who might be his father. Since it was kind of unclear whether or not it was Bob or John. There was something said about a blood test having been done with John when Adrian was younger. But there was a comment about John's sample not being received in a timely fashion and how Adrian's mother never got any results. Yet saw John with some paperwork with results, but didn't really see the whole results, as far as whether or not he was Adrian's father.

And being those tests would've been done so long ago, technology in DNA has greatly improved. Was nothing said of having new testing done? Just going by looks alone, Adrian looked more like Bob than John. Even though Adrian and John had similar dispositions/personalities though. And it was quite clear his mother wasn't sure of which really was his father. Yet John believed he was the father.

So who really is Adrian's father? Cause I didn't see any definite answer on that. It just made it seem as if John was his father and that was that.