Jean Gray and April O'Neil are actually the same person. Her spirit is split in half, and half is in April, while the other is Jean. Which is why the Phoenix force is able to live in Jean

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Jean Gray and April O'Neil are sisters. Their mom, trying to save them, tried opening a portal using Kraang technology. It worked, but their mother only had enough time to get Jean through. Jean's real last name is O'Neil.

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Jean and April are twin sisters, however, there was a complication during birth. The mutagen reacted badly to x-gene in Jean's body, so they (their parents) needed to send her somewhere where mutagen didn't affect mutants. Thrus, opening the portal to the X-men universe.

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Special thanks to HowlettTwins for somewhat giving me the idea! ^-^