Kate Middleton can be playful and naughty, too.

The Duchess of Cambridge was first seen at a royal engagement in 2006 when she was a guest at Prince William’s passing-out parade after he completed his training at the military academy Sandhurst. According to royal biographer Andrew Morton in his book “William and Catherine,” the duchess uttered a cheeky comment during the event.

Middleton was seen leaning over her mother when Prince William marched past and said, “I love the uniform. So, so sexy.”

The author noted that the event was also a big day for Middleton because it was the first time she appeared at an official royal engagement. The duchess made a distinctive debut in a broad-brimmed black hat, black boots and vibrant red coat which was reminiscent of one of Princess Diana’s outfits.

“The comparisons with the late Diana, Princess of Wales, who had once worn a similar outfit, were inevitable, and would continue for the foreseeable future, even as Kate began to become a style icon in her own right,” the author added.

Meanwhile, Middleton’s mom Carole was criticized for chewing a piece of gum during the event. Many felt that she was disrespecting the ceremony and the sovereign for doing so. It reinforced some commentators to say that Middleton didn’t have “breeding” to become Queen.

Middleton made heartbreaking sacrifices to marry Prince William. Her friends felt that she gave up her independence for conformity and her adventure for safety when she decided to become a royal.

When the Duke and Duchess of Cambridge split in 2007, many of her friends were happy and relieved because they saw how she changed when she started dating Prince William. She also stopped seeing her friends which really upset them. However, it didn’t take long for the couple to rekindle their romance.

Earlier this year, there were rumors that Prince William cheated on Middleton with a family friend named Rose Hanbury. If Prince William and Middleton were to divorce, the latter will lose her HRH title but will remain the Duchess of Cambridge.

Kate Middleton Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge attend the traditional Easter Sunday church service at St George's Chapel, Windsor Castle on April 21, 2019 in Windsor, England. Photo: Getty Images/Max Mumby