expression, noun
prince on a white horse; Prince Charming
Refers to an idealized romantic hero, often used in the context of a woman's dream partner. The phrase is a set expression and not used literally.
彼女はいつか白馬の王子が現れると信じている。
She believes that someday her Prince Charming will appear.
A calque from Western fairy tales, literally 'prince of the white horse'. The exact origin in Japanese is uncertain, but it became a common idiom for an idealized romantic partner.