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John Cena just learned that Darren Young came out as the first openly gay WWE superstar ... and Cena tells TMZ he couldn't be happier for the guy.

"Oh wonderful," Cena said ... "I know Darren personally. Darren's a great guy. That's a very bold move for him. And congratulations for him for actually finally doing it."

Cena says he's proud of his friend ... especially because he has a brother who is gay and he knows how tough it can be to come out.

As for the WWE, Cena says he doesn't think the organization will care one way or the other -- and that's a good thing.