In the Flash Season 6 episode "A Flash of the Lightning," The Monitor reveals to Barry Allen that he must die on December 10, 2019, to save billions, forcing a confrontation with the accelerated Crisis on Infinite Earths timeline [Wikipedia]. Barry, along with Jay Garrick, experiences a vision of the future that confirms the necessity of this sacrifice, leading him to accept his fate after failing to breach a speed force barrier [Arrowverse Wiki]. For more details, visit the Arrowverse Wiki page for "A Flash of the Lightning."
