 Mattaboy was scheduled to face To-Agori-Mou and Kings Lake in the St James's Palace Stakes at Royal Ascot but was withdrawn after being found to be running an abnormally high temperature on the morning of the race.He reappeared in the Sussex Stakes at Goodwood on 29 July but ran poorly and finished seventh, thirteen lengths behind the winner Kings Lake.He was then sent to race in the United States where he was trained by Peter Howe.