The nature of the lithium enrichment in the most Li-rich giant star

About 1% of giant stars(1) have anomalously high Li abundances (A(Li)) in their atmospheres, conflicting directly with the prediction of standard stellar evolution models(2). This finding makes the production and evolution of Li in the Universe intriguing, not only in the sense of Big Bang nucleosynthesis(3,4) or the interstellar mediums(5) but also for the evolution of stars. Decades of effort have been put into explaining why such extreme objects exists(6-8), yet the origins of Li-rich giants are still being debated. Here, we report the discovery of the most Li-rich giant known to date, with a very high A(Li) of 4.51. This rare phenomenon was observed coincidentally with another short-term event: the star is experiencing its luminosity bump on the red giant branch. Such a high A(Li) indicates that the star might be at the very beginning of its Li-rich phase, which provides a great opportunity to investigate the origin and evolution of Li in the Galaxy. A detailed nuclear simulation is presented with up-to-date reaction rates to recreate the Li enrichment process in this star. Our results provide tight constraints on both observational and theoretical points of view, suggesting that low-mass giants can internally produce Li to a very high level through Be-7 transportation during the red giant phase.