Marie Juliette Louvet (May 9, 1867 - September 24, 1930) was mistress of Prince Louis II of Monaco and was the mother of his only child, Princess Charlotte of Monaco.

Known as Juliette, Louvet was the daughter of Jacques Henri Louvet (1830 - 1910) and his first wife, Joséphine Elmire Piedefer (1828-1871).

She married photographer Achille Delmaet on October 6, 1885 (his best known photographs are nudes of La Goulue, a cancan dancer of the Moulin Rouge). The Delmaets were divorced on January 14, 1893; they had two children, Georges (1884-1955) and Marguerite (1886-1894).

Juliette Louvet became an entertainer of sorts, reportedly a cabaret singer (other sources identify her as a laundress and a dressmaker), then was Prince Louis' lover. She gave birth to their daughter, Charlotte, in Algeria on September 30, 1898.