Excerpts from Books and Wikipedia
"However, in the spring of 1542 he died of a fever, still only in his early forties. In order to continue the ruse of de Soto's divinity, his body was secretly sunk in the Mississippi in the middle of the night. The first Spanish exploration of the American Southeast now complete, the expedition built boats and sailed down the Mississippi to Mexico. Despite their efforts, the territory would be taken over by the French in the seventeenth century." [1001 Days]