Why Kate Middleton's royal wedding dress was the "nicest gesture" for her future sister-in-law.

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Everyone knows the only dress you’re meant to focus on at a wedding is the bride’s.

Not hard to do when the wedding is the royal wedding, and the bride is former actress Meghan Markle.

But while most of us were focused on Meghan’s classic Givenchy boat neck, long sleeve gown by British designer Clare Waight Keller, a hardworking journalist noticed something familiar about The Duchess of Cambridge, Kate Middleton’s dress.

That’s because she’s worn it before. Twice.

Kate wearing a dress she has worn TWICE before. Charlotte’s christening and the Queen’s birthday. #RoyalWedding
Truly the nicest gesture she could show her now sister-in-law. Absolutely nothing to see here! Focus on the bride! pic.twitter.com/WQ0Vq8QfB0

— Elizabeth Holmes (@EHolmes) May 19, 2018

“Kate wearing a dress she has worn TWICE before. Charlotte’s christening and the Queen’s birthday. #RoyalWedding. Truly the nicest gesture she could show her now sister-in-law. Absolutely nothing to see here! Focus on the bride!” journalist Elizabeth Holmes posted on Twitter.

The first time Kate wore the long sleeved, off-white coat dress was to celebrate Queen Elizabeth II’s 90th birthday in June 2016.

The second, at daughter Princess Charlotte’s christening the following month in July, 2016.

To be honest, we think the mum-of-three has enough on her plate without rustling up a new royal wedding outfit, no?

Or maybe baby Prince Louis threw up on her first choice and she had to go with option B.

Guess we'll never know.

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For more royal wedding content, the Mamamia Out Loud team have huddled together for a raw, unedited, and slightly inappropriate Royal Wedding debrief. Get it in your ears.