NEW YORK : David Letterman’s final ‘Late Show’ appearance after decades in the hot seat will be on May 20, CBS television said Wednesday. ‘David Letterman has given to all of us a remarkable legacy of achievement and creative brilliance that will never be forgotten,’ said Leslie Moonves, president of CBS. ‘It’s going to be tough to say goodbye, but I know we will all cherish the shows leading up to Dave’s final broadcast in May.’ The 67-year-old entertainer announced in April that he would retire from the ‘Late Show.’