What is the origin of insouciant?

Insouciant, “free from concern or anxiety; carefree; nonchalant,” comes straight from French insouciant, literally “not caring,” a compound of the French negative prefix in– “not” (from Latin in-, and naturalized in English in– from both Latin and French borrowings), and the present participle souciant “caring,” from the verb soucier “to trouble, care.” Soucier comes from Vulgar Latin sollicītāre “to worry, vex,” from Latin sollicitāre “to disturb, harass.” The French noun souci “care, worry” is part of the phrase sans souci “without worries, carefree,” which, spelled Sanssouci, is the name of the summer palace built by King Frederick the Great, King of Prussia, in Potsdam, between 1745 and 1747. Insouciant entered English in the first half of the 19th century.