Eclipse Award winner Countess Diana, whose Breeders' Cup win remains the third-largest margin of all time, was euthanized over the Memorial Day weekend at Rood and Riddle Equine Hospital near Lexington. The 11-year-old daughter of Deerhound had undergone surgery for the account of insurance underwriter Lloyd's of London.Kentucky-bred Countess Diana was an easy choice for 1997 champion 2-year-old filly after winning the Breeders' Cup Juvenile Fillies (gr. I) by 8 1/2 lengths at Hollywood Park, which remains a record for the race. The victory came for her breeder, Richard S. Kaster, and his wife, Nancy, and for Kaster's sister, Nancy, and her husband, Donald Propson. Patrick Byrne saddled her.Countess Diana began her racing career for trainer Carlos A. Garcia. She won in track-record time of :51.50 for 4 1/2 furlongs at Pimlico in her debut, after which she was transferred to Byrne. Countess Diana's other wins her 2-year-old season came in the Spinaway Stakes (gr. I) by 6 1/2 lengths, the Walmac International Alcibiades Stakes (gr. II), and the Schuylerville (gr. II) Stakes.Countess Diana's weight assignment on the 1997 Experimental Free Handicap for fillies reflected her Breeders' Cup dominance. Countess Diana was assigned high weight of 125 pounds. The weight remains the second-highest ever for a topweighted filly, surpassed only by First Flight's 126 pounds in 1946.Byrne left after Countess Diana's 2-year-old season to train for Frank Stronach. Trained at three by Bill Mott and at four by Mary Jo Lohmeier, Countess Diana won twice and ran second in the Nassau County Stakes (gr. III) from eight starts those two years. She was retired with seven wins from 14 starts and earnings of $1,117,185.Countess Diana, who was produced from the T. V. Commercial mare T. V. Countess, was sold at the 2000 Keeneland January horses of all ages sale. Kenny Troutt and Bill Casner, owners of newly formed WinStar Farm near Versailles, Ky., bought her for $1.8 million from Eaton Sales, agent.As a broodmare, Countess Diana produced four named foals, one of which, Mama Nadine, is stakes-placed. Her last two offspring are unnamed--a Gone West yearling colt and an Elusive Quality colt foaled March 22. The latter was bred by Racehorse Management, a division of WinStar, and is at the farm.