Kept in training as a four-year-old, Mill Reef returned to Longchamp to win the Prix Ganay in April 1972 by ten lengths (though photographs of the finish make it closer to twelve lengths). A summer rematch with Brigadier Gerard, who had also been kept in training as a four-year-old, was earmarked for the Eclipse Stakes at Sandown. But after a narrow win in the Coronation Cup at Epsom Downs, by a neck from Homeric, Mill Reef was found to be suffering from a heavy virus, and the rematch had to be postponed.