The Grand Preceptor, the Grand Tutor and the Grand Protector were together called the Three Dukes.
Tips
history
Under the Zhou the three were 太师, 太傅 and 太保. Under the Western Han they were 丞相, 太尉 and 御史大夫; under the Eastern Han, 太尉, 司徒 and 司空.
usage
In today's news 三公 means the three kinds of official spending the public watches most: trips abroad at public expense, 公车 'official cars' and 公务 receptions. Their budget is the 三公经费.