Kate Middleton against Pippa: Friendly rivalry

Duchess of Cambridge Kate Middleton and her suddenly-famous younger sister Pippa may be best friends, but that doesn't mean they're unlike most siblings.

"There is a healthy competition between the two," royal watcher Katie Nicholl tells Us. "Certainly when it comes to looks, there is a little friendly rivalry."

Kate and Pippa Middleton also squabble over "weird things," says a family source. "You'd see them fight over who had the worst headache or period pain!"

Okay. We're all about Pippa and Kate, but that's just TMI.