I, Claudius - Season 1 Episode 13

AD 54: Claudius feels that Rome should return to be a Republic but nonetheless marries his niece Agripinilla and makes her son Nero co-heir with his own, teen-aged son Britannicus. Aware of a prophecy that Nero will indeed become sole emperor Claudius encourages Britannicus to flee abroad and then return to restore the Republic but the boy refuses and he is killed by Nero. Claudius resignedly allows himself to be poisoned by his wife and dies. Nero and Agripinilla look for his will but find only his chronicle which they burn. However Claudius and the Sibyl have the last laugh as he has made a copy, which he has buried to be found long after his death.