I similarly ended up with a half brother I didn't know I had, but we didn't find him with DNA. My Dad did something with a lady back in college, well before he met mom. They parted ways and he never knew she ended up pregnant, she gave the baby away. Fast forward 35 years and he goes looking for his biological parents. All he knew was bio-mom's name and what college she attended. He finds her, contacts her, and they reunite, and then they contact my Dad.
So my Dad and my half-brother meet and spend about a year getting acquainted with each other, then one day Dad sits me and my other four siblings down and says, "You each have an older half brother you didn't know about."
He lived about four hours away so we eventually planned a trip up to meet him. I still remember pulling up to the house, him walking out, and me seeing him for the first time. I said to my husband, "He is the spitting image of my Uncle Bob." (Dad's brother.) No DNA test needed, there is no doubt he's Dad's. We have become very close, we couldn't be closer if we'd grown up together.