Father of 3 children turns out to have been infertile all his life.

The rest of the conversation 

The thought of him not being his sons’ real father had broken Richard. He was one lump of emotion. His son put a hand on his shoulder and said something incredible. Full of strength and love, he reassured his father: “You may not be my biological father, but you are still my dad.” 

The two gave each other a big hug, but Richard was still devastated by the news.