Charli xcx's setting up for Brat Summer without the "t" in 2026 ... stripping down to just a bra for a sexy photo shoot she posted Friday.

The pop star shared a couple black-and-white photos to Instagram in which she's lying on the bed ... the straps of her bra pulled down her shoulders -- and a hand tastefully hiding her nipple as she stares up into the camera.

There's no grin on Charli's face ... she's going for sultry here -- and totally owning the post, we gotta say.

She captioned the post, "london… tomorrow night?" -- though it's unclear to what she's referring. Charli's not currently on tour, so it doesn't appear to be a show, but we'll just have to wait and see. The move comes days after Madonna called her out for making the claim that dance is dead.

Charli's been more involved in film than music this year ... she's starred in and produced the newly released -- a mockumentary in which Charli plays herself that skewers the modern music industry.

She did release a new album ... but even that was in service to film -- a soundtrack for Emerald Fennell's "Wuthering Heights" flick starring Jacob Elordi and Margot Robbie.

Anyhoo ... English fans should rejoice -- Charli's in town, and the London Bridge covering her chest is falling down!