The TV star, 37, pulled out all the stops when she appeared as the Wicked Fairy in Sleeping Beauty which kicked off on Friday (11 December).
Sharing a shot of her stunning costume with her two million Twitter followers, Katie simply wrote: "Woooo [...] Here we go."
Unsurprisingly, Katie's costume was shocking pink, with huge gold horns - the trademark of Princess Aurora's nemesis Maleficent.
She also shared a photo before her dramatic transformation, where she is relaxing backstage in her onesie - yep, pink again!
Katie is appearing at Woking's New Victoria Theatre where EastEnders legend Anita Dobson is also sharing the role of the fairytale villain.
CBeebies favourite Ben Faulks (aka Mr Bloom) stars as Prince Charming.
Katie was photographed leaving the theatre with her husband Kieran Hayler and their daughter Bunny after the opening night performance.
Meanwhile, her fans were quick to tell the star what they thought of the show.
One commented: "Just got back from the performance, personal opinion: you and the rest of the cast were fantastic."
Another said: "Wow Katie, your costume looks amazing and you look amazing in it. Loving all the pink. You go girl. Xxx."
Speaking about her panto role previously, the author said: "I'm not sure who's more excited about my role in panto, me or the kids!
"They're going to enjoy it so much seeing me up on stage, although they might find it strange that I'm being so evil.
"Sleeping Beauty is one of the kids' favourite stories and I simply couldn't resist the opportunity. The people of Woking better watch out as I'm coming to getcha!"
Katie will be starring as the Wicked Fairy until Sunday 27 December, with Anita taking over afterwards.
To be honest, the feathers, sequins and bold pink are standard attire for mum-of-five Katie!
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