A Klingon raid on the Federation research outpost at Doctari Alpha during Michael Burnham's childhood, in which her father was killed and her mother vanished into the far future.
Mike and Gabrielle Burnham worked at Doctari Alpha on a secret Section 31 project, a time-travel suit powered by a rare time crystal. They had stayed on at the outpost a few days longer so that their daughter could watch a nearby star go supernova.
Klingons, drawn by the crystal, attacked the station. Michael hid in a cupboard and heard the assault. Her father died, and her mother escaped in the suit, intending to jump back an hour but instead becoming anchored some 950 years in the future.
The raid is first mentioned in The Vulcan Hello. The Discovery episodes The Red Angel and Perpetual Infinity show it directly and reveal that the Section 31 officer Leland's carelessness led the Klingons there.