The 22-year-old star put on a very busty display as she attended the launch of Madison White Forest's winter Terrace which was sponsored by CîROC Vodka.
Demi opted for a floor-length black dress which featured velvet panels and lots of sheer material.
The garment’s plunging neckline left very little to the imagination and also featured a thigh-high split.
Demi posed up a storm as she arrived at the rooftop party and was more than happy to flash the flesh.
Her dark locks were pulled back into a sleek ponytail and Demi completed her look with a pair of black strappy heels.
Demi was joined at the party by former Made in Chelsea star Kimberley Garner.
The 27-year-old blonde also put on a racy display as she arrived wearing a barely there gold minidress.
The chainmail garment allowed Kimberley to flaunt her never-ending pins, which she elongated with a pair of matching stilettos.
Perhaps feeling the winter weather later on, Kimberley covered up in a khaki duster coat as she headed home in black taxi.
The former reality star later posted a snap of herself at the rooftop bar with St Pauls in the background and simply captioned it: “beautiful london.”