Automorphisms of moduli spaces of principal bundles over a smooth curve

For any almost-simple group Formula: see text over an algebraically closed field Formula: see text of characteristic zero, we describe the automorphism group of the moduli space of semistable Formula: see text-bundles over a connected smooth projective curve Formula: see text of genus at least Formula: see text. The result is achieved by studying the singular fibers of the Hitchin fibration. As a byproduct, we provide a description of the irreducible components of two natural closed subsets in the Hitchin basis: the divisor of singular cameral curves and the divisor of singular Hitchin fibers.