We determined the rupture sequence of the Aug 12, 2021 Mw 8.2 South Sandwich Island earthquake which, according to the reports from the National Earthquake Information Center, appears to be a complex sequence in both time and space. Notable tsunamis were recorded by tide gauges at global distances. Given the complexity of this event, we used a multiple subevent inversion method that can accommodate complex variations of fault geometry, location, depth, and temporal characteristics of the event. We found that the rupture initiated as a regular deep thrust earthquake; it then triggered a shallow dominantly slow subevent extending ~200 km to the south, and ended with 2 other regular subevents. The total duration is ~260s, unusually long for an Mw 8.2 event. Our result is qualitatively consistent with other moment tensor solutions and the observed mB-Mw and MS-Mw relations, and provides a more quantitative space-temporal pattern of this unusual sequence.