A reverse startup procedure for a multi terminal smart transformer (MTST) supplying data centres, transitioning from islanded operation to grid connected operation is proposed in this paper. During islanded operation, the MTST low voltage (LV) converter remains active, while the MTST multi active bridge (MAB) converter is partially active and MTST medium voltage (MV) converter is inactive. To facilitate reconnection to the MV grid from the LV side, these converters need to be activated to allow the power flow. In this operation, the power is drawn from a battery energy storage system (BESS) connected to LVdc-1 bus to charge the MTST MVdc bus. Once the MVdc bus is sufficiently charged, the MTST-MV converter is initiated to establish the connection between the LV side and the MV grid. Simulation is performed in PSCAD and the results are provided to validate the effectiveness of this startup operation.