10 Greatest Unspoken Star Wars Movie Plot Points
2. Darth Plagueis' Ashes Are Stored Outside Palpatine's Office - Revenge Of The Sith
You may or may not recall that, outside of Supreme Chancellor Palpatine's office, there are two impractically large black vases placed on either side of the door.
To the casual observer these vases would appear to be merely ornamental, though the 2012 reference book Star Wars: Beware the Sith reveals that the vases are actually spirit urns.
Canonically the urns have been used to store important items, and in this case Beware the Sith reveals one of them to contain the ashen remains of Palpatine's own departed Sith Master, Darth Plagueis.
That's certainly a bold move on Palpatine's part, and though Beware the Sith is technically now part of Star Wars' Legends continuity, like most Legends lore fans are free to debate its canonicity until explicitly stated within the new canon.
Given that the spirit urns are also mentioned in 2017's Visual Encyclopedia book, which is 100% canon, it seems unlikely that their status as Plagueis' final resting place will ever be directly contradicted in any new Star Wars media.