Nab Kate Middleton's Perfect Holiday Frock Before It Sells Out—on Sale Now!

We're all getting in the Christmas spirit: the holiday is less than a week away! Kate Middleton just became our holiday fashion goals across the pond on Monday, taking to The Mix Christmas Party in a festive frock from Vanessa Seward ($623, originally $1,245; net-a-porter.com).

Few have mastered the long-sleeve midi dress like the Duchess of Cambridge, but it was interesting to see her gravitate toward the French brand, as she normally opts for designs from L.K. Bennett. The stunner's gorgeous floral print was offset by a timeless black, waist-cinching belt and black pumps. She joins a long list of stylish women who love Seward's pieces, including Michelle Williams and Katie Holmes. And luckily for us all, it's available right now on sale. Though we know that won't last long, as anything the duchess wears sells out almost immediately.

She was joined by husband Prince William and brother-in-law Prince Harry at the youth support service's holiday celebration—an organization that aids youth under 25 in the UK with advice about drugs, jobs, mental health, money, and more. The trio will not only be joining breakout sessions, but will also take part in a live online counseling chat, as well as speaking to volunteers and The Mix users.

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Later today, there will be a Christmas party reception where the Princess and Princes will get to meet the service's outstanding volunteers. There will also be The Mix Annual Awards, in which the triumvirate will present the Volunteer of the Year Award.

The only thing we regret is Meghan Markle not being by Prince Harry's side here. As an activist and humanitarian, this would have been a great event for her. Perhaps next time ...