The Prisoner of Zenda (1952)

English trout fisher Rudolf Rassendyll is about the only tourist not coming for the coronation of Central-European King Rudolf V at Strelsau, but happens to be a distant relative and is approached because of their uncanny resemblance to stand in for the drunken king, in order to prevent his envious half-brother Michael, who arranged spiking his wine, to seize the throne when the reputedly less-then-dutiful Rudolf stays away. The ceremony goes well, and he gets acquainted with the charming royal bride, related princess Flavia, but afterward it's discovered that the king has been abducted; he must continue the charade and once the hiding place, the castle of Zenda, is found is involved in the fight between political parties for control over Rudolf V, his throne and his bride, for which a formidable third candidate, Michael's disloyal co-conspirator Rupert of Hentzau, was waiting in the curtains.