Al Hasawi took to Twitter to inform Forest fans Cox had joined the club, tweeting: "Welcome to Republic of Ireland international striker Simon Cox, who has joined us from West Brom. He is our seventh signing of the summer."
Cox also used Twitter to express his excitement that he was a Forest player, tweeting: "Think I'm all done now. Signed now. Can't wait to get started and exciting times ahead #nffc.
"I would like to thank all the fans and players and staff at WBA for my time there loved it. Met some lovely people. Wish u all the best."
Forest begin their season with a televised Capital One Cup tie against Fleetwood Town on Monday, August 13.