• Kate Middleton wore a red tartan dress by Emilia Wickstead in a new video she and Prince William shared Monday
  • An expert said there is an "unwritten rule" in the style world that red, tartan plaids are "reserved for the holiday season"
  • But the editor noted that style rules are made to be broken

Kate Middleton's tartan outfit in a recent video had some fans and fashion experts wondering if the duchess may have broken a winter fashion "rule."

On Monday, the Duke and Duchess of Cambridge thanked the hospital staff at NHS Tayside for their work in a video they shared on social media on Burns Night, Scotland's celebration of poet Robert Burns. In the video, Middleton is wearing a $3,700 Emilia Wickstead red tartan dress—a style choice fashion experts recommend avoiding outside the month of December.

Brittany Talarico, People magazine's senior style editor, noted that while there is an "unwritten rule" in the style world about not wearing plaid beyond the Christmas season, these rules aren't set in stone.

"It's an unwritten style rule that red, tartan plaids are reserved for the holiday season. Kate's look feels more 'Christmas card' ready and less 'January Zoom' appropriate," Talarico told People.

"However, just like white after Labor Day, 'style rules' are made to [be] broken," she continued. "And seeing how cheerful the print looks, Kate's commitment to plaid might just start a fashion revolution. Now, can we talk about her straight, shiny hair?"

The mom-of-three may have chosen the dress because its pattern is closely associated with Scotland, People noted. Middleton has been known to wear tartan pieces whenever she visits the country.

In December, when the Duke and Duchess of Cambridge carried out their train tour of the U.K. and stopped by Edinburgh, Scotland, Middleton was photographed wearing a tartan scarf.

Meanwhile, Prince William and Middleton's Instagram followers had nothing but praise for the royal couple.

"Ah...the world's favorites! So lovely to see," one commented.

"Best couple ever," another wrote with red heart emoji.

"You two are amazing," a third user said, while another wrote, "William and Kate look amazing as always!"

The Duke and Duchess of Cambridge also remembered the public and the frontline workers on Christmas Day. They shared several photos on social media commemorating the year as they wish for a better 2021.

"This Christmas our thoughts are with those of you who are spending today alone, those of you who are mourning the loss of a loved one, and those of you on the frontline who are still mustering the energy to put your own lives on hold to look after the rest of us," the Cambridges wrote on Twitter.

They continued, "Wishing a merry Christmas doesn’t feel right this year, so instead we’re wishing for a better 2021."

Kate Middleton
Kate Middleton arrives to launch a new national support line at the charity Family Action on Jan. 22, 2019 in Lewisham, England.  Getty Images/Adrian Dennis