The former X Factor contestant stepped out in London's West End to watch The Commitments musical and looked glam in an all-black outfit with a hint of blue from her slightly exposed bra.
While showing off your underwear can be risky business, given that it seems to be a hot trend this year (Myleene Klass gave us a glimpse of her knickers last week!) we can't fault Katie for having a go.
And since the rest of her ensemble is understated and simple, the blue bra doesn't actually look that bad!
Katie teamed her bra with a black vest top, a leather pencil skirt and peep-toe heels.
She also swept her short blonde hair to one side finished off her look with a bright red lipstick.
Giving her sexy image a rock 'n' roll edge were her various tattoos, which includes a large portrait of a pin-up girl on her upper arm and a new tattoo tribute to her mum.
Also on The Commitments red carpet yesterday evening (8 October) were fellow X Factor star Amelia Lily and Made In Chelsea's Cheska Hull, who looked chic in a camel coat.
Since leaving the popular ITV singing competition, Katie has been busy working on new music as part of a group called Red Velvet.
She even tied the knot in an intimate ceremony in the States last year, but she and hubby Brad Alphonso split up just 10 weeks later.
What do you think of Katie's red carpet outfit? Let us know below, as the best comment each week wins £50!