When, by fraud or fraudulent concealment, a party against whom a claim for relief exists prevents the person in whose favor such claim for relief exists from obtaining knowledge thereof, the latter may commence an action within one year from the time the claim for relief is discovered by the latter or might have been discovered by the latter in the exercise of diligence. Such fraud or fraudulent concealment must be established to the satisfaction of the court or jury, as the case may be, by a fair preponderance of the evidence.