Using femtosecond time-resolved resonant magnetic x-ray diffraction at the Ho L 3 absorption edge, we investigate the demagnetization dynamics in antiferromagnetically ordered metallic Ho after femtosecond optical excitation. Tuning the x-ray energy to the electric dipole ( E 1 , 2 p → 5 d ) or quadrupole ( E 2 , 2 p → 4 f ) transition allows us to selectively and independently study the spin dynamics of the itinerant 5 d and localized 4 f electronic subsystems via the suppression of the magnetic (2 1 3 − τ ) satellite peak. We find demagnetization time scales very similar to ferromagnetic 4 f systems, suggesting that the loss of magnetic order occurs via a similar spin-flip process in both cases. The simultaneous demagnetization of both subsystems demonstrates strong intra-atomic 4 f − 5 d exchange coupling. In addition, an ultrafast lattice contraction due to the release of magneto-striction leads to a transient shift of the magnetic satellite peak.