The East End is mourning the loss of a beloved chef found dead on a Southampton beach.A man and his daughter were walking on Wyandanch Lane Beach yesterday morning when they found the body of 35-year-old Keith Greene. Investigators believe he drowned.The Hampton Bays man appeared on the Fox reality show "Hell's Kitchen" in 2006. He was also a chef at Schmidt's Market in Southampton Village and had worked at several other Hamptons hot spots over the years.Police: Body found in Southampton; possible drowning