Kate Middleton's Royal-Blue Dress Already Sold Out

Princess-to-be starts a fashion frenzy for the Issa dress she wore at her engagement announcement

It's been two days since the big announcement, and Kate Middleton is already seeing the power she has on the public.

The blue Issa London dress the princess-to-be wore to meet the press with Prince William on Tuesday—which played off her sapphire ring beautifully, natch—is selling out fast!

Department store Harvey Nichols' buying director Averyl Oates told Vogue U.K. that the long-sleeve frock, which costs around $620, had "sold out at [the department store] within hours of the images going live.

"Since the announcement of the royal engagement we have been inundated with requests regarding Issa," he added.

Only style icons like Princess Diana, Carolyn Bessette-Kennedy and, more recently, Michelle Obama, have sparked this kind of fashion frenzy.

What couture will come next? Bring it, Kate!