STLtoday.com

Wife’s sister apparently

Let’s break down what the relationship would be to the offspring of that union. A boy would be Tony’s son and his nephew and his wife’s nephew and her stepson. A girl would be his daughter and his niece and his wife’s niece and her stepdaughter. It gives a new meaning to the old song, entitled “I’m my own Grandpa”.

According to USA today it was wife's sister.