Charles le mauvais.Charles II of Navarre (1332–1387).
He is gone to the bad.
Has become a ruined man, or a depraved character. He has gone
amongst bad people, in bad ways, or to bad circumstances.
To the bad.
On the wrong side of the account; in arrears.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894