The Tichborne Claimant (1998)

The wealthy Tichborne family send servant Bogle to Australia to track down their missing heir. He doesn't find the lost Sir Roger, but comes up with a false claimant whom he trains to act aristocratic in return for half of any eventual inheritance. All seems to be going well until the dowager Tichborne dies suddenly and the family start to get suspicious. They expel the claimant, but he takes his case to the High Court, where the truth of the missing heir is revealed.