Later in the year Aggressor was beaten at York and Ascot[2] but won the Doonside Cup at Ayr and finished third to London Cry in the Cambridgeshire Handicap.

[5] At Royal Ascot in June, Aggressor produced his best performance to date, beating the 1959 Epsom Derby winner Parthia in the Hardwicke Stakes.

The 2/5 favourite for the race was Prince Aly Khan's filly Petite Etoile, winner of the 1000 Guineas, Epsom Oaks, Sussex Stakes and Coronation Cup.

Ridden by Jimmy Lindley, Aggressor, who was well-suited by the rain-softened[7] ground went to the front in the straight and held off the challenge of Petite Etoile in the closing stages to win by half a length.

[9] In their book A Century of Champions, John Randall and Tony Morris rated Aggressor a "poor" winner of the King George VI and Queen Elizabeth Stakes.

[11] Aggressor's daughter Aggravate (who won the Park Hill Stakes) was exported to Walter Jacobs's Fährhof Stud (near Bremen, Germany), where she foaled among others the German champion-racehorse and leading sire Acatenango.