Sleep Deprived Rihanna Signs On for VMAs Performance

Getting another day underway in the UK, Rihanna was spotted exiting her posh London hotel on Tuesday (August 28).

Wearing denim hotpants teamed with a pair of leopard print high heels and a green ballcap, the Barbadian beauty stepped out after failing to get her hoped-for beauty sleep, as she tweeted, "It's 430 am and I'm up like an idiot! Can't sleep! Whyyyyyyy????!!!"

Meanwhile, RiRi's back and forth with Joan Rivers on Twitter has now drawn TV personality Kelly Osbourne into the fray.

Sending a message to Rihanna on Miss Rivers' behalf, Osbourne messaged, "w/ the greatest of respect 2 a young lady of whom I love please get a sense of humor @Joan_Rivers paved the way 4 all us opinionated ladies!"

Also of note, it was just announced that the 24-year-old - as well as Frank Ocean - will be among the performers at the 2012 VMAs when the show air lives on September 6th beginning at 8/9c on MTV.

Enjoy the pictures of Rihanna heading out in London (August 28).