Kate Middleton is an 'ultimate trooper' for attending royal ceremony while battling cancer, says expert.

Kate Middleton is putting on a brave face.

Despite her ongoing battle with cancer, the Princess of Wales made her first public appearance in months to attend the Trooping the Colour event. A royal expert who was present at the ceremony shares that Middleton's attendance makes her "the ultimate trooper."

Catherine's style resembled Audrey Hepburn's in "My Fair Lady" as described by Kinsey Schofield on the "To Di For Daily" podcast, who noted that she wore a white knee-length dress with navy accents, a matching hat, and white heels for the event.

"Catherine was described as porcelain by one person in the crowd. She was particularly engaged with the children in the carriage. The crowd roared when the King's carriage approached and peaked when they realized that Catherine was close behind."

As the family returned to Buckingham Palace in their carriage, the rain came down so hard on the crowd that the family visibly reacted. The children definitely felt some sympathy!

Despite the rain, there was probably an increase in attendance following Catherine's announcement yesterday.

"Schofield told Planet Chronicle Digital that Catherine is a leader and expressed his sadness that she felt the need to appear on TV amidst the ongoing speculation and misinformation online, especially during bad weather. He added that she is a true trooper."

Middleton's attendance at Trooping the Colour signifies her first public appearance since Christmas and her first royal event since revealing her cancer diagnosis in March.

She shared on social media yesterday that she was making progress in her chemotherapy treatment, but that there were good days and bad days. On the bad days, she felt weak, tired, and needed to rest. On the good days, she felt stronger and wanted to make the most of feeling well.

My treatment is ongoing and will continue for a few more months. On days when I feel well enough, engaging with school life, spending personal time on things that give me energy and positivity, and doing a little work from home bring me joy.

The princess acknowledged that she is "not out of the woods yet," but said she is "looking forward" to today's event. She also hopes to attend "a few public engagements over the summer."

I am learning how to be patient, especially with uncertainty. I am taking each day as it comes, listening to my body, and allowing myself to take this much needed time to heal.

The annual event of Trooping the Colour, which celebrates the monarch's birthday, takes place in June, regardless of their actual birthday. The ceremony involves the presentation of the military's flags or "colours."

According to Christopher Andersen, author of "The King," King Charles II initiated the very first Trooping the Colour in the 1600s.

"According to Andersen, the date of the parade was changed from November to June due to King Edward's preference for better weather. Since then, it has been held on either the first week, the first Saturday in June, or the second Saturday in June."

At the event, Middleton was captured on camera riding in a carriage with her husband, Prince William, and their children, Prince Louis, Prince George, and Princess Charlotte, as well as King Charles and Queen Camilla, posing for photos on the palace balcony.

Planet Chronicle Digital's Stephanie Nolasco contributed to this report.