Looking for Half Brother-Born in Baltimore 1963 to 1966

I am looking for a possible half brother that I recently found out about. After telling my brother that my father had a half brother, he shocked me by telling me that we also had a half brother. He said that my father had a relationship with a woman before he met my mother which produced a son. If this is true, it would have had to have occurred prior to 1966 when my parents were married. My brother only told me that my father was very young. He seemed to think that the child remained with the mother. The only other thing he said was that my father ran into the child's mother some years ago in a department store. Any help would be greatly appreciated. I am not necessarily looking for a reunion. I have always been interested in family history. I would love to know if this individual is OK and that they have had a good life like my father has given us. I am shocked that he never said anything about this, especially since he is extremely family oriented and always wondered why his own father abandoned him. My father's name is Donald L. Grimm. He was born in 1946 in Pennsylvania and came to Baltimore sometime in the 1950's. I believe this child would have been born sometime between 1963 and 1966. My father lived on Echodale Avenue and attended Poly. I would assume the mother would have been from the neighborhood. My dad went to Poly. Thanks, Shane