  It is found that de-Sitter spacetime, the constant-curvature matter-free
solution of the Einstein equations with a positive cosmological constant,
becomes classically unstable due to the dynamic effects of a certain type of
vector field (fundamentally different from a gauge field). The perturbed
de-Sitter universe evolves towards a final exotic singularity. The relevant
vector-field configurations violate the strong and dominant energy conditions.
