chassez le naturel, il revient au galop

Etymology
"Drive off character, it comes back galloping", a quote from the drama "Le Glorieux" (1732) by Philippe Néricault, also named. Likely inspired by a similar phrase by in his 10th epistle: "Naturam expelles furca, tamen usque recurret." ("Though you drive out nature with a pitchfork, she will keep coming back.")

Proverb

 * 1) a leopard cannot change its spots