F-regularity of large Schubert varieties

Let G denote a connected reductive algebraic group over an algebraically closed field k and let X denote a projective G × G-equivariant embedding of G. The large Schubert varieties in X are the closures of the double cosets BgB, where B denotes a Borel subgroup of G, and g ε G. We prove that these varieties are globally F-regular in positive characteristic, resp. of globally F-regular type in characteristic 0. As a consequence, the large Schubert varieties are normal and Cohen-Macaulay.