During her first solo royal engagement, Kate Middleton displayed for the first time glimpses of a previously unknown scar from an unknown childhood cause.

According to palace sources, the three-inch scar was from a childhood operation. However, they refrained from revealing much, citing privacy.

The prominent scar was quite visible on the side of her left temple during the event at Clarence House.

The scar could have been from anything, including a birthmark, trauma, neurosurgery or a benign growth of the skin. You can't tell any  more than that, Dr. Roy Geronemus, director of the Laser & Skin Surgery Center of New York, told ABC.

During the black-tie event, Kate, 29, looked stunning in a silver evening gown by designer Amanda Wakeley. As per reports, the vintage gown is from the designer's Winter 2006 collection.

The Duchess conducted the event on behalf of her father-in-law, Prince Charles. Apparently, the prince had to travel to Riyadh to offer his condolences to the Saudi royal family following the death of Crown Prince Sultan.