LEXINGTON, Ky. - Conquistador Cielo, whose dramatic Metropolitan Mile-Belmont Stakes double in just five days propelled him to the 1982 Horse of the Year title and a record syndication price, died Tuesday morning at Claiborne Farm in Paris, Ky. The Mr. Prospector horse foundered in his left foreleg, and Claiborne officials decided to euthanize him. Conquistador Cielo was 23.