None other than Glee's Lea Michele!
Stephenson says Kate could take a tip from the way Michele manages to strike a balance between looking both youthful and elegant at the same time.
"I have to say, I was talking to Lea in the front row at Alexander Wang and I like that shes not about showing it all off," she told E! News. "I love that she's a little more demure in a time when everyone is taking their clothes off. She's wearing beautiful, feminine, chic clothes and it's like Kate Middleton can take a nod from Lea, because I think Kate Middleton has so many eyes upon her and sometimes I think she's a little too adult. And I know the pressures and Lea kind of does that perfect elegance but still stays young."
Stephenson said it was the way Lea wore her Alexander Wang dress that she bought off the rack that caught her attention.
"She was wearing an Alexander Wang dress that she actually saw in the store here for Fashion's Night Out so she threw it on," she told us. "She was sitting front row and she looked gorgeous. I think that she's kind of like that; she still is such a lady for such a young girl and I love that."
Other than Prince William's lady, who else does she think could use a little help in the fashion department?
"Besides Snooki? I want to single-handedly go in and make over the entire Jersey Shore," she laughed. "Can we do that?"