Looks like it was both a great and a rough weekend in London for Katy Perry. After the 'Wide Awake' singer was spotted with reported rekindled flame Robert Ackroyd, she planned to catch up with her buddy Justin Bieber across the pond. But she got so drunk that she allegedly fell over in a nightclub and needed to be carried out. NSFW photos of Perry, flashing a bit of a fleshy butt cheek, have surfaced from the night. Looks like she threw one (or five) too many back while having a good time.

Perry, who performed at the star-studded Capital FM Summertime Ball over the weekend, hit Cirque du Soir and had a few drinks while hanging out with fellow raven-haired diva Jessie J. The Biebs and Ackroyd were also on site.

The fashionable diva, dressed in a short, black and white patterned outfit and black fishnet thigh highs, flashed her rump more than once -- her skirt was hiked up super high while a friend helped her out of the venue.

She reportedly partied until 5AM and sipped too many cocktails. Allegedly, bottles of vodka and champagne were on her table. Yikes. That's a recipe for one really horrific hangover. We hope her assistant or Ackroyd got her plenty of aspirin and water in the aftermath.

An insider told The Daily Mirror (quotes courtesy of Entertainment Wise) that Perry was in "high spirits and very excited that Justin was there, as she loves Justin. And she's good friends with Jessie, so they had a catch-up. Before long Katy had sunk a fair few vodka cocktails. She had big bottles of Ciroc and Belvedere on her table."

With all that alcohol at her disposal, Perry was wobbly and couldn't stand on her own two legs. The insider said, "By 5AM, she seemed to be having some difficulty walking and suddenly fell to the floor. She was down for a while and it took a couple of her mates to get her up. Everyone was staring and there was quite a commotion."

Katy is one of the busiest pop stars on the planet. She's allowed to let off some steam, let loose and have some fun. We're just a little shocked to see her look so sloppy in public.