MCU: Every Character Confirmed For Phase 4 (So Far)
23. Ayesha

Confirmed By: James Gunn, who told IGN: "I absolutely plan on bringing Elizabeth Debicki back."
High Priestess Ayesha has some seriously unfinished business with the Guardians of the Galaxy, and there's no way you can introduce her creation Adam without bringing her back too.
As she's already been in one movie it's unlikely the character will stick around beyond Vol 3, but we should expect to see her unleashing Adam on the Guardians as a means of revenge, and it's quite possible her own creation will turn against her too.
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