An American celeb just broke every royal protocol.

It’s the Kate effect.

The Duchess of Cambridge continues to fly  the flag for British fashion during her tour of the US – today wearing a popping pink coat from Mulberry.

Unsurprisingly, the $2800 double-breasted has already sold out online. Bad luck for anyone wanting to emulate Kate's look.

The Royal couple are wrapping up a very busy few days in the US. Today, Kate and Will, both 32, first paid their respects at the 9/11 memorial site. They laid a wreath with a handwritten note reading, “In sorrowful memory for those who died on 11 September and in admiration of the courage shown to rebuild.”

The couple then visited two of New York City's leading youth organisations - The Door and The CityKids - where they watched the kids perform. Lunch was a reception with members of the British arts community. The busy couple then visited the Empire State Building, which was lit up with the colours of the Union Jack in honour of their visit.

In the evening Kate and Will were the guests of honour at a fundraising dinner at the Metropolitan Museum of Art, held to raise funds for their 600-year-old alma mater, the University of St Andrews.

A number of celebrities were also in attendance, including Sir Patrick Stewart, who said, "I have met many members of the Royal family before but what a personable, pleasant and, may I say, attractive couple.

"Prince William told me he had never been to New York before which, I must say, surprised me greatly. I was even more surprised that the Duchess hasn't been. I urged them to come back again incognito. New York is the type of city that turns a blind eye and would allow you to do that."

We'd love to see Kate and Will in some fake moustaches and big sunglasses.

But it was an incident that occurred the previous evening at a Basketball game that has "courted" some controversy. Famous basketball player LeBron James posed with Kate and Will and completely broke royal protocol ... he put his arm around Kate. Shock, horror!

During the game, the Royal couple broke our celebrity brains by chatting with American "royalty" Beyonce and Jay Z.

After a jammed back few days, we bet the couple are glad they'll be reunited with bub Prince George by tomorrow morning.

No word on whether they will be catching a commercial flight (like Will did yesterday, much to the surprise of passengers).

Ok guys, now it's time to visit Australia again. Please!

CLICK THROUGH the gallery to see what the Royal couple have been up to and wear they've been staying...

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Kate Middleton shows off her growing baby bump.

Excited fans greet Kate and Will for the start their royal tour.