There is no official reference to Quantum Rex in the Kingdom Hearts series, nor is there any evidence that Xehanort has knowledge of it. However, if you’re referring to a fan theory, crossover speculation, or an extended universe concept, it would depend on the context.

Possible Explanations:

  1. Quantum Mechanics and Kingdom Hearts – Kingdom Hearts plays with concepts of multiple realities, time travel, and parallel existences, which could be linked to “quantum” ideas. Xehanort’s ability to manipulate time and foresee future possibilities might loosely relate to a “Quantum Rex” concept if it involves a multiversal or time-traveling entity.
  2. Fan-Theory or Non-Canon Material – If Quantum Rex is part of a fan-theory, extended lore, or an unrelated media reference, then it would be outside the official Kingdom Hearts storyline.
  3. Cross-Universe Speculation – If Quantum Rex is a reference to another Square Enix property or a hidden concept, there could be fan speculation connecting it to Kingdom Hearts through multiversal travel, something Xehanort would theoretically be aware of.