  Almost hypercomplex manifolds with Hermitian and Norden metrics and more
specially the corresponding quaternionic Kaehler manifolds are considered. Some
necessary and sufficient conditions the investigated manifolds be isotropic
hyper-Kaehlerian and flat are found. It is proved that the quaternionic Kaehler
manifolds with the considered metric structure are Einstein for dimension at
least 8. The class of the non-hyper-Kaehler quaternionic Kaehler manifold of
the considered type is determined.
