CHELTENHAM, UK—With a slightly surreal sense of the final day of the Cheltenham Festival providing a last hurrah for racing as know it, at least for now, Al Boum Photo (Fr) (Buck's Boum {Fr}) returned to the scene of his greatest triumph to land back-to-back runnings of the Magners Cheltenham Gold Cup. He's not seen often, but when the sleek 8-year-old gelding appears at the races he seldom disappoints and his assured victory sealed a sensational day for Willie Mullins, who saddled the first four winners of the week's finale....