  Proximity effects induced in the 2D Dirac material graphene potentially open
access to novel and intriguing physical phenomena. Thus far, the coupling
between graphene and ferromagnetic insulators has been experimentally
established. However, only very little is known about graphene's interaction
with antiferromagnetic insulators. Here, we report a low temperature study of
the electronic properties of high quality van der Waals heterostructures
composed of a single graphene layer proximitized with $\alpha$-RuCl$_3$. The
latter is known to become antiferromagnetically ordered below 10 K. Shubnikov
de Haas oscillations in the longitudinal resistance together with Hall
resistance measurements provide clear evidence for a band realignment that is
accompanied by a transfer of electrons originally occupying the graphene's spin
degenerate Dirac cones into $\alpha$-RuCl$_3$ band states with in-plane spin
polarization. Left behind are holes in two separate Fermi pockets, only the
dispersion of one of which is distorted near the Fermi energy due to spin
selective hybridization with these spin polarized $\alpha$-RuCl$_3$ band
states. This interpretation is supported by our DFT calculations. An unexpected
damping of the quantum oscillations as well as a zero field resistance upturn
close to the N$\'e$el temperature of $\alpha$-RuCl$_3$ suggests the onset of
additional spin scattering due to spin fluctuations in the $\alpha$-RuCl$_3$.
