  We have obtained the most general solution of the Einstein vacuum equation
for the axially symmetric stationary metric in which both the
  Hamilton-Jacobi equation for particle motion and the Klein - Gordon equation
are separable. It can be interpreted to describe the gravitational field of a
rotating dyon, a particle endowed with both gravoelectric (mass) and
gravomagnetic (NUT parameter) charge. Further, there also exists a duality
relation between the two charges and the radial and the polar angle coordinates
which keeps the solution invariant. The solution can however be transformed
into the known Kerr - NUT solution indicating its uniqueness under the
separability of equations of motion.
