  We present direct local-probe evidence for strongly hybridized
nuclear-electronic spin states of an Ising ferromagnet LiHoF$_4$ in a
transverse magnetic field. The nuclear-electronic states are addressed via a
magnetic resonance in the GHz frequency range using coplanar resonators and a
vector network analyzer. The magnetic resonance spectrum is successfully traced
over the entire field-temperature phase diagram, which is remarkably well
reproduced by mean-field calculations. Our method can be directly applied to a
broad class of materials containing rare-earth ions for probing the
substantially mixed nature of the nuclear and electronic moments.
