The quasi-biennial oscillation (QBO) is a repeating cycle of tropical stratosphere winds reversing direction from eastward to westward roughly every 14 months. Discovered independently by British and American scientists the QBO continued undisturbed for 27 cycles from 1953 until February 2016 when a westward jet unexpectedly formed in the lower stratosphere during the eastward phase. This disruption is attributed to unusually high wave momentum fluxes from the Northern Hemisphere. A second, similar, QBO disruption occurred during the 2019/2020 northern winter though this time the Arctic polar vortex was exceptionally strong and wave fluxes weak. Here we show that this latest disruption to the regular QBO cycling was twice as strong as that seen in 2016 and resulted from horizontal momentum transport from the Southern Hemisphere. The disruption began in September 2019 when there was a rare Southern Hemisphere sudden stratospheric warming followed by abnormal conditions in the stratosphere with the smallest ozone hole since its discovery and enhanced equatorward momentum fluxes. In both disruptions the normal downward progression of the QBO halts and the eastward shear zone above the disruption moves upward assisted by stronger tropical upwelling during the boreal winter. Results from the two disruptions provide compelling evidence of a fundamental change in our understanding of the dynamics of the QBO with extra-tropical influences more significant than previously thought. In turn, this implies a less predictable QBO. Furthermore, the expected climate response of the mechanism we have identified suggests that reoccurring QBO disruptions are consistent with an emerging signal of climate change weakening QBO amplitudes as predicted by models.