Lady GaGa made a surprise appearance at gay club G-A-Y in London last night (26.10.13).

The 'Do What U Want' singer, who is in the British capital ahead of a TV performance on 'The X Factor' this evening (27.10.13), shocked fans with an unannounced stage performance at the popular hotspot late Saturday night.

Gaga appeared to be getting into the Halloween spirit, clad in all white, with long, white hair and pale make-up.

The chilling look did little to scare fans away, however, as the raucous crowd welcomed the singer to the stage for an impromptu performance of her new song 'Venus'.

She wrote on Twitter after the appearance: ''Had an amazing night tonight at G-A-Y in London, after all these years you continue to inspire me. Can't wait for X-Factor tomorrow night! (sic)''

It appears Gaga's performance was kept tightly under wraps as club promoter Jeremy Joseph declared her visit the ''hardest secret'' he's ever had to keep.

He tweeted: ''How incredible is @ladygaga, the hardest secret I've had to keep, sooooo happy, quadruple wow

''I think I've proved tonight, I can keep a secret, Wish I could that every week

''I've just woken up, had this really odd dream that I was on stage at G-A-Y with a naked Lady GaGa (sic)''