Lion and the True Prince
(The). The lion will not touch the true prince (1 Henry IV., ii. 4). This is a religious superstition; the “true prince,” strictly speaking, being the Messiah, who is called “the Lion of the tribe of Judah.” Loosely it is applied to any prince of blood royal, supposed at one time to be hedged around with a sort of divinity.
Fetch the Numidian lion I brought over; If she be sprung from royal blood, the lion Will do her reverence, else he'll tear her.
Beaumont and Fletcher: The Mad Lover.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894