Gabrielle copied the "Control" hitmaker's clothes and hair - and even her trademark mole - to give her what she thought was an edge over the other hopefuls, and she was stunned when the real Janet walked in and sat down opposite her.
"Everyone and their mother was auditioning for 'The Matrix'," she told "The Late Late Show With James Corden". "I went to audition [and] I needed to feel like the most powerful, beautiful and amazing woman in the world, so of course, I wanted to channel Janet Jackson."
"I go to Extensions Plus, which is, like, the Mecca of [hair] waves. I wanted to get the good hair, the Janet hair, from the weave emporium. I literally find the exact outfit from her album cover. I draw in the d**n mole. I fully committed. I play Janet the whole time, waiting for the audition, in there early. No one's going to stop me…[and] in walks Janet Jackson."
"The same audition, and I'm cosplaying as Janet, with a weird drawn-on mole. Neither of us got it. I think we canceled each other out."
When the two stars crossed paths later at a Miami, Florida nightclub, Union wasn't sure she wanted to meet the singer after their embarrassing audition moment, but the singer's then-boyfriend, Jermaine Dupri, told the "Bring It On" star Jackson wanted to say hello, and the starstruck actress burst into tears.
"I'm bawling in the club, snot bubbles, the whole thing... but now she knows I'm a weirdo," Gabrielle recalled. "I don't know what's about to happen, and I get there, and she jumps up and gives me a hug and says, 'I'm so proud of you...!' Now we're friends."