Joan O’Brien, the wife of retired Thoroughbred trainer Leo O’Brien and the mother-in-law of Hall of Fame jockey John Velazquez, died Thursday night after a two-year battle with cancer. She was 75. Joan and Leo O’Brien were married for 54 years. They had two children, a daughter, Leona, and son, Keith. Leona married John Velazquez in 1994. The couple has two children. Keith O’Brien worked as an assistant for his father for several years before taking over the small stable two years ago. Keith and his wife, Deirdre, have five children. “Absolutely gut-wrenching loss for our family,” Keith O’Brien said. “She meant everything to us. She was the glue that kept everybody together.” Keith O’Brien said there will be a traditional Irish wake at the family home on Monday with a burial scheduled for Tuesday. Velazquez, who has been based in Southern California this winter, has been in New York this week to be with the family. Velazquez will ride Saturday at Oaklawn and then not again until next week.