[ch = k]. The hero of John Bunyan's allegory called The Pilgrim's Progress. He flees from the “City of Destruction,” and journeys to the “Celestial City.” He starts with a heavy burden on his back, but it falls off when he stands at the foot of the cross.
Pepin le Bref was so styled by Pope Stephen III. (714-768).
Charles le Chauve was so styled by the council of Savonnières (823, 840-877). Louis XI. was so styled by Pope Paul II. (1423, 1461-1483).
Since which time (1469) it was universally adopted in the French monarchy.
“And thou, O Gaul, with gaudy trophies plumed, `Most Christian king.' Alas! in vain assumed.”
Camoens: Lusiad, book vii.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894