Just found out my dad had another kid before I was born

Yeah so long story short I was scrolling through old family stuff and found some letters. My mom confirmed it after I asked her about it. Apparently my dad's teenage girlfriend had a kid and gave him up for adoption before my parents got together. This was in the 80s. My dad never told any of us and now I'm sitting with this weird info. Not mad, just processing I guess. Anyone else have family skeletons like this?