[1] This prosperity ended with the publication in 1720 of his Philippiques, odes accusing the regent, Philip, duke of Orléans, of the most odious crimes,[1] such as committing incest with his eldest daughter, Marie Louise Élisabeth d'Orléans, Duchess of Berry, a debauched young widow rumored to have hidden several pregnancies by her father and who died at age 23, her health prematurely destroyed by her secret maternities.

[citation needed] Lagrange might have escaped the consequences of this libel but for the bitter enmity of a former patron, the duc de La Force.

He found sanctuary at Avignon, but was enticed beyond the boundary of the papal jurisdiction, when he was arrested and sent as a prisoner to the Île Sainte-Marguerite.

He was part author of a Histoire de Périgord left unfinished, and made a further contribution to history, or perhaps, more exactly, to romance, in a letter to Élie Fréron on the identity of the Man with the Iron Mask.

"If the author has a sense of theater and dramatic situations, the characters are cold and false and versification is hard and prosaic" (Gustave Vapereau).