What is the equitable principle of fraudulent concealment?

The equitable principle of fraudulent concealment was described by Dickson J. in Guerin v. The Queen, 1984 CanLII 25 (SCC), [1984] 2 S.C.R. 335, at p. 390: [W]here there has been a fraudulent concealment of the existence of a cause of action, the limitation period will not start to run until the plaintiff discovers the fraud, or until the time when, with reasonable diligence, he ought to have discovered it. The fraudulent concealment necessary to toll or suspend the operation of the statute need not amount to deceit or common law fraud.