A good chunk of this prophecy was fulfilled this week in “The Wrath of Savitar.”
Certainly, in retrospect, it’s a betrayal; as keeping that shard proved to be Savitar’s salvation from whatever pocket hell in the Speed Force Barry eventually trapped him in.
The other betrayer could be tormented Wally, since he’s the one who ends up flinging the shard into the Speed Force, thus giving Savitar the way out of his cage.