Kate's three inch scar can be seen in her hair on her left temple as she shakes hands with a guest at Clarence House.

Kate Middleton, the Duchess of Cambridge, has a three-inch scar, mostly hidden in her hair above her left temple, and it peeked through her half-up, half-down hairdo as she hosted her first solo engagement.

A spokesperson for St. James’ Palace, where William and Kate keep their official office, said the scar was related to a childhood operation.

When pressed for more details, the spokesperson declined to elaborate, citing Kate’s privacy.

Unnamed sources told The Daily Mail that it was a “very serious operation,” but would not go into further detail.

This is the first time the scar had been noticed since Kate catapulted into the spotlight after she met Prince William at St. Andrew’s University in 2001, and it left many wondering about the cause.

“The scar could have been from anything, including a birthmark, trauma, neurosurgery or a benign growth of the skin,” said Dr. Roy Geronemus, director of the Laser & Skin Surgery Center of New York. “You can’t tell anymore than that.”

Aside from her headline-making scar, Kate’s first solo event as a royal went flawlessly.

The Duchess of Cambridge stepped in at the last minute to take over the hosting duties of her father-in-law, Prince Charles, who had flown to Riyadh to offer his condolences to the Saudi royal family following the death of the Crown Prince of Saudi Arabia.

The private, black-tie dinner took place at Clarence House, where patrons of the Prince’s charity, In Kind Direct, mingled with the future queen.

One of the Prince of Wales’ many charities, In Kind Direct helps facilitate donations from companies with excess merchandise and passes the goods along to charitable causes.

Kate was seen in photos from the dinner, mingling easily with guests and wearing a stunning Amanda Wakeley silver gown with a beaded halter neck.

However, it wasn’t Kate’s fashion, but rather the knowledge she brought to the dinner that impressed Robin Boles, the chief executive of the charity, who said in a statement posted on the Prince of Wales’ website: “The Duchess hosted a very special evening with absolute professionalism and charm.”