The blonde singer kept her famous sibling's identity a secret when she appeared before judges Simon Cowell, Cheryl Fernandez-Versini, Louis Walsh and Mel B.
Simon, however, was pretty sure he knew her…
"Have we met before?" he asked, prompting Lizzy to quip: "Maybe in your dreams?!|"
Lizzy explained that she used to work as a receptionist and had recently landed a job as a personal assistant.
She then belted out her audition song – and secured four yeses! We wonder what the judges will think when they learn who her mega famous brother is?!
Well, we already know Simon was none too happy he wasn't informed beforehand!
"I don't like to know anything [before someone auditions]… but there was a girl that came in who turned out to be Robert Pattinson's sister," he said recently. "They [production] didn't tell us, and in fact she didn't tell us until afterwards, which was a bit annoying.
"But I don't like to know. [It's more fair that way]."
Watch Lizzy's audition:
Lizzy was said to have kept her brother's identity a secret from the X Factor crew on purpose as she wanted to succeed on her own merit.
A source told The Mirror: "She didn't mention she was related to him to any judges or producers. It's important to her she does not fall into the trap of just becoming Rob's sister."
Twilight heartthrob Rob has said he's bursting with pride about his sister's success.
"I'm so ridiculously proud of her," he's been quoted as saying. "I would never have the balls to do it in a million years. I can't believe she's done it. It's amazing."
X Factor continues Saturdays and Sundays on ITV.
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