The singer-songwriter is among thousands who have performed in front of judges Simon Cowell, Cheryl Fernandez-Versini, Louis Walsh and Mel B in the hopes of getting to this year's live shows.
R-Pattz is quoted in The Sun as saying: "I'm so ridiculously proud of her. I would never have the balls to do it in a million years. I can't believe she's done it. It's amazing."
We'll have to wait until the new series airs later this year to see if Lizzy's audition will be among those shown on the programme – and if she makes it through to the elusive judges' houses and live shows.
X Factor returns for its 11th series at the end of this month. The first trailer was released this week showing the judges involved in a Game of Thrones-style battle for success.
Lizzy, 31, is the older sister of Twilight heartthrob Rob, 28, but sources say she didn't use her famous surname to get ahead.
"She didn't mention she was related to him to any judges or producers," a source told The Mirror. "It's important to her she does not fall into the trap of just becoming Rob's sister."
Watch X Factor's Game of Thrones themed trailer below:
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Cheryl's X Factor career in highlights:
Copyright: REX/Ken McKay