Daniel Amneus argued that Macbeth as it survives is a revision of an earlier play, in which Duncan granted Macbeth not only the title of Thane of Cawdor, but the "greater honor" of Prince of Cumberland (i.e. heir to the throne of Scotland).
The text suggests that Daniel Amneus believes the current version of Macbeth is a modified version of an earlier play where Duncan bestowed upon Macbeth not only the title of Thane of Cawdor but also the "greater honor" of Prince of Cumberland, which indicates he was destined to be king.