Emperor Palpatine's claim in Star Wars: The Rise of Skywalker that he'd become "All ... ancient knowledge and dark secrets of the past, Darth Sidious angered his Sith predecessors.

Speaking of the planet Darth Sidious sent those soon to be dead Separatists ... Former Master and Apprentice and brothers-turned-enemies Anakin Skywalker and Obi-Wan Kenobi crossed lightsabers ...