  Using femtosecond time-resolved photoelectron spectroscopy we demonstrate
that photoexcitation transforms monoclinic VO$_2$ quasi-instantaneously into a
metal. Thereby, we exclude an 80 femtosecond structural bottleneck for the
photoinduced electronic phase transition of VO$_2$. First-principles many-body
perturbation theory calculations reveal a high sensitivity of the VO$_2$
bandgap to variations of the dynamically screened Coulomb interaction,
supporting a fully electronically driven isostructral insulator-to-metal
transition. We thus conclude that the ultrafast band structure renormalization
is caused by photoexcitation of carriers from localized V 3d valence states,
strongly changing the screening \emph{before} significant hot-carrier
relaxation or ionic motion has occurred.
