"During a daily ride on October 20, 1934, Bess suffered a brain haemorrhage and died almost immediately. The colonel buried her where she collapsed and had a memorial cairn erected as a mark of respect for a truly remarkable horse," Mr Macdonald said.
"This year marks the centennial of the start of World War 1 and many events are being held to celebrate this anniversary. The service for Bess is registered as one of these," he said.
Michael Powles, the colonel's grandson, will be among the guests at next Friday's service, as will the Colonel's 1928 Sunbeam Talbot. The Friends of Bess will be holding a three-day horse trek from a woolshed in Forest Rd and riders from around the North Island have registered.
Mr Macdonald said the Friends will be holding a morning tea for all attending the service at the woolshed.
The Bulls Museum had set up a static display about Bess.