  We present the first experimental observation of K$_{\beta}$ emission from
highly charged Mg ions at solid density, driven by intense x-rays from a free
electron laser. The presence of K$_{\beta}$ emission indicates the $n=3$ atomic
shell is relocalized for high charge states, providing an upper constraint on
the depression of the ionization potential. We explore the process of state
relocalization in dense plasmas from first principles using finite-temperature
density functional theory alongside a wavefunction localization metric, and
find excellent agreement with experimental results.
