British pop star Lily Allen is "exhausted" after her gruelling U.S. tour, according to her father Keith Allen .
Actor Keith admits the singer is struggling in America on her own - and insists the public aren't aware how tough being a top pop star really is.
He says, "She's completely exhausted."
"It's really hard, that f**king industry. People don't realise how f**king mind-numbing it is."