The 39-year-old actor said that it was his father's ring and he was not married, reported Daily Mirror.
"You know when they take a picture and it becomes a negative image That was my father's ring. I am not married," he said.
The couple have been together for 18 months.
Cooper also revealed that he spent three hours a day in the gym for his role as Chris Kyle in 'American Sniper', the story of a marine who killed over 150 terrorists.
"I bulked up and gained 40lb I ate 5,000 calories a day. It was brutal," he added.