K0-anti-K0 mixing in the 1/Nc expansion

We present the result for the invariant B_K factor of K0-anti-K0 mixing in the chiral limit and to next-to-leading order in the 1/Nc expansion. We explicitly demonstrate the cancellation of the renormalization scale and scheme dependences between short- and long-distance contributions in the final expression. Numerical estimates are then given, by taking into account increasingly refined short- and long-distance constraints of the underlying QCD Green's function which governs the B_K factor.