No wonder Simon Cowell recognised her at her X Factor audition - she's only Robert Pattinson's big sister! Say hello to singer Lizzy Pattinson

She baffled Simon Cowell when she walked into her audition on The X Factor on Sunday night: ‘Have we met before?’ he asked.

‘Only in your dreams,’ the blonde joked. But there’s a very good reason why Simon, 54, might recognise Lizzy Pattinson – she’s only Robert Pattinson‘s big sister!

As all hardcore R-Pattz fan’s know, his beaufitul sister Elizabeth is a professional singer.

Rather than trade on her brother’s success and contacts though, Lizzy, 31, chose to keep quiet about her famous little brother during her audition in front of judges Simon, Cheryl Cole, Mel B and Louis Walsh.

Instead the judges put her through to boot camp on her own singing merit – and she gained the respect of Cheryl and Mel B for giving Simon a bit of backchat in the process.

A source said: ‘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”.’

So, what else is Lizzy keeping secret?

1. Rob is massively proud of her

When news leaked that Lizzy had secretly auditioned for The X Factor, her brother couldn’t contain his pride.

The notoriously private Twilight actor, 28, said: ‘I’m like 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.’

2. She is fiercely protective of her lil bro…especially when it comes to Kristen Stewart

Lizzy grew close to Robert’s ex girlfriend Kristen Stewart during the course of their rocky four-year relationship – and even spent Thanksgiving with K-Stew after news broke that she had cheated on Rob with married film director Rupert Sanders.

She was there for him when he tried to make their relationship work – and, according to sources, supported him to follow his heart rather than listen to what everyone else was telling him to do.

We wonder what she makes of his new girlfriend FKA Twigs?

3. She sang on the Twilight soundtrack

Lizzy sings backing vocals on the track Who Are They? in the first Twilight film, when Edward Cullen appears in the cafeteria.

She said: ‘I feel honoured to have been a part of the film, albeit a very small part. It was so much fun!’

You can hear her singing here:

4. She has already had a hit in the charts

In 2003 Lizzy released a song with German duo Milk & Sugar. The song Let the Sunshine In made it into the top 20 in the UK. Yeah, us neither. Listen to it here:

5. Rob is her ‘inspiration’

Lizzy says that when she’s on stage Rob is her ‘inspiration’. We’re not quite sure what that means, but it’s cute all the same.

SEE PICTURES Robert Pattinson and Kristen Stewart – a love story in photos