  We derive a charged black hole solution in four dimensions described by
$SL(2,R)\times SU(2)\times U(1)/U(1)^2$ WZW coset model. Using the algebraic
Hamiltonian method we calculate the corresponding solution that is exact to all
orders in ${1\over k}$. It is shown that unlike the 2D black hole, the
singularity remains also in the exact solution, and moreover, in some range of
the gauge parameter the space-time does not fulfil the cosmic censor
conjecture, $i.e.$ we find a naked singularity outside the black hole. Exact
dual models are derived as well, one of them describes a 4D space-time with a
naked singularity. Using the algebraic Hamiltonian approach we also find the
exact to all orders $O(d,d)$ transformation of the metric and the dilaton field
for general WZW coset models and show the correction with respect to the
transformations in one loop order.
