The Essex singer was snapped on the red carpet ahead of her performance with Clean Bandit, where they performed new tune 'Tears' for the first time.
And it was clearly the perfect opportunity for Louisa to show off her makeover - we can't believe how different she looks!
We're used to seeing the star working a girl-next-door-image and long blonde locks, but it's all changed. Switching up her barnet, Louisa's ditched the beachy golden strands for an edgy lilac mane.
Her newly coloured hair was styled into long tumbling waves for a Mermaid style 'do. Pretty cool, right?
Louisa's outfit was also different from the types of get-ups we saw her wearing on the X Factor. Forget girly dresses and sparkly tops, the 18-year-old opted for a thigh-skimming bodycon dress that was embellished with a bold array of beads and embroidery.
Adding a pair of black caged heels to the ensemble, Louisa looked fierce for her show at Wembley Stadium.
As well as singing with Clean Bandit, Louisa also joined Nathan Sykes on stage for a surprise duet of 'Over and Over'. Made up with how her performances went, Louisa tweeted afterwards, saying: "What an amazing day. @cleanbandit i love you! And @NathanSykes thank u so much for letting me join you on stage! (sic)".
Louisa was crowned the winner of last year's X Factor in December, beating fellow finalists Reggie 'N' Bollie.