Selena Gomez & Niall Horan: Still Deny Banging, But Still Partying Together

Selena Gomez and One Direction's Niall Horan left the 'X Factor' finale after-party within seconds of each other Sunday night in London -- doing ZERO to help her claim that they're NOT dating.

Selena even hung backstage after 1D performed during the finale. Odd, since just days ago she insisted there's no romance between them and they're just friends.

For some reason, she tried to hide her face from photogs outside -- even though she'd already been seen hanging at the show. Maybe she's just in de-Niall?