Dislocation motions in crystals govern the plasticity even under high strain rate deformations induced by shock waves. The maximum speed at which dislocations can move inside crystals have been controversial and a key unsettled question is whether dislocations can move faster than the transverse speed of sound or not. While many theoretical studies predicted that dislocations would not move faster than the speed of sound, some of the recent theoretical and molecular dynamics simulation works suggest that such ultrafast dislocation motions are possible. In this talk, we discuss about our in-situ X-ray radiography (with some phase-contrast effect) results which captured shock-induced stacking faults in single-crystalline diamond extending faster than the transverse sound speed of diamond. This is an indirect evidence of patrial dislocations at the edge of stacking faults moving faster than the sound speed of diamond. Our experiments were conducted using the X-ray Free Electron Laser (XFEL) at SPring-8 Angstrom Compact Free Electron Laser (SACLA). By using the femtosecond XFEL pulses and a lithium fluoride crystal detector, we can obtain in-situ X-ray radiography with a >10^6 dynamic range and ~1-µm spatial resolution over a wide field of view of > 1-mm. Understanding the shock-induced ultrafast dislocation behaviors is important to accurately model the deformation under these extreme conditions.