Not me, but I had a friend with a brother who was a year younger, and when they got in a huge fight, he told him he was adopted.
I'm not sure why a parent would let a kid make it to 16 and hide that type of secret.
Side note, I have an aunt that I didn't know was adopted until I was 30. Looks just like her sisters, and I never asked until she mentioned it as she felt less than her sister.