Duchess Catherine showed more than some skin at a charity event last night in London -- she also revealed a big scar on her head!

The 3-inch scar was spotted on Kate Middleton's left temple at an event for In Kind Direct, her first public appearance without her royal husband, Prince William, by her side.

St. James Palace tells the Daily Mail that the scar is a result of "a childhood operation," but didn't elaborate.

Kate's dress definitely distracted from the mark! Wearing a gorgeous Amanda Wakeley gown, she bared more skin than we're used to seeing.

With her arms, shoulders and collarbone exposed, she looked stunning!

Check out the gallery above for some of the Kate's best looks.

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