The supernova that destroyed Romulus in 2387, after the Federation abandoned Picard's rescue effort.
In the late twenty-fourth century, a star near Romulus was expected to go supernova and threaten the Romulan homeworld. The Romulan Star Empire turned to the Federation for help, and Admiral Jean-Luc Picard led an effort to build a vast fleet of rescue ships to evacuate millions of Romulans.
In 2385 synthetic workers attacked the Utopia Planitia shipyards on Mars, where the rescue fleet was being built. The Federation responded by banning synthetics and cancelling the rescue, and Picard resigned in protest. As Star Trek: Picard later revealed, the attack had been arranged by the secret Romulan group the Zhat Vash.
In 2387 the star exploded, destroying Romulus. Ambassador Spock tried to stop the shockwave with red matter but was too late, which led to Nero's revenge in the 2009 film. The surviving Romulans were scattered, and the Empire broke apart. Characters seen in Picard, such as the former Tal Shiar agents Laris and Zhaban and the young warrior Elnor, live in the aftermath.