When you're friends with the future Queen of England, you've got a lot to tell, and Kate's gal pal Emma Sayle is spilling the beans.
William's brother, Prince Harry, has the reputation of being a party boy. But Sayle told INSIDE EDITION's Diane McInerney that William and Harry are very much alike in that department.
"Prince William is a cad," said Sayle. "He's a ladies man, but he's not going to cheat on Kate. But he's flirtatious and he's out and about."
"Harry's got that cheeky look about him. William doesn't look like it, but he's out and about as much as Harry is," said Sayle.
Sayle and Kate became friends during the time Kate and William temporarily split. Kate seemed to be having the time her life, showing up at one Halloween party in a skimpy witch outfit. She also showed lots of leg after one night on the town.
McInerney asked, "Was Kate devastated by the breakup?"
"She was devastated. Everything she had done before had been with William. She handled it well with her head held high," said Sayle.
Sayle and Kate were on the same rowing team and took shopping trips together. Sayle said she learned there had been sibling rivalry between Kate and her sister Pippa during boarding school. The sisters even had a competition to see who could lose the most weight.
"There was a bit of a weight war going on," said Sayle.
"Kate and Pippa had a weight war going on?" asked McInerney.
"Yes, they had a big one," replied Sayle.
But Sayle says talk that Kate might be anorexic is ridiculous.
"I don't think she has an eating disorder. What bride doesn't lose a few pounds when you know you're going to be watched by people around the world?" said Sayle.
Kate and Sayle have gone their separate ways, but Sayle believes Kate will follow in the late Princess Diana's footsteps.
"Kate will talk to anyone and she is very kind and not snooty at all. Diana was the People's Princess and that's what I think Kate is very much the modern day people's princess," said Sayle.