Captain Mark Phillips has agreed to design the cross country course at Rockingham Castle International Horse Trials.
Previously known as Brigstock Horse Trials, the event next May will be the third held at the castle.
Captain Phillips has already been for a walk around the site and plans are under way, with several changes to the layout already being discussed.
Event organiser Andrew Norman said: “We are thrilled to have Mark Phillips on board.
“His courses are highly regarded by competitors who have already given the event their vote of approval over the past two years.
“This is the perfect news for us as we strive to make the Rockingham Castle Horse Trials a ‘must go to’ event both for riders and spectators.”
The horse trials takes place at Rockingham Castle from May 22 to May 24.