She's my half-sister and I only knew I had a sister when my mother found out my Dad had a lover 4 years ago and he already had a daughter with her. When I knew the story my first thought was that I would like to meet my half-sister. She was 20 when we first met and I was 23 and she's very, very open minded. So open minded we fucked for the first time, two weeks after we met. Now she calls me her full service half-brother and treat her the same.