Kate Middleton made a sustainable fashion statement at Trooping the Colour.

The Princess of Wales, 42, joined the royal family at King Charles’ official birthday parade in London on June 15, marking her first public event in six months after she announced in March that she has cancer and is undergoing chemotherapy.

At Trooping the Colour, Princess Kate arrived wearing a white Jenny Packham dress with black trim and ribbon embellishment on the neckline. While it appeared to be a new piece in her closet at first, the outfit was actually an upcycled version of the ensemble that the royal wore last year on the eve of King Charles’ coronation. The simple white and black dress was updated with a new neckline and different details around the waist.

This time around, Kate wore her hair swept into an updo beneath a white hat by Philip Treacy. She accessorized with earrings that appear to be her Cassandra Goad Cavolfiore Pearl Studs — which she previously wore to Prince Louis’ christening in 2018 and Wimbledon in 2023 — and the Irish Guards Regimental Brooch, nodding to her role as the regiment’s honorary colonel, which is trooping its “colour” (or flag) today.

Kate Middleton attends a Buckingham Palace event on May 5, 2023. Toby Melville – Pool/Getty Images

She traveled by carriage in the Glass Coach with Prince George, 10, Princess Charlotte, 9, and Prince Louis, 6, before she will join the royal family on the Buckingham Palace balcony later in the day.

Kate Middleton arrives at Trooping the Colour on June 15, 2024. JUSTIN TALLIS/AFP via Getty

For last year’s Trooping the Colour, she wore a bright green dress by Andrew Gn with a matching hat by Philip Treacy. Gn grew up in Singapore, and Princess Kate’s outfit choice was seen by some as a nod to the location of Prince William’s Earthshot Prize awards that year.

She completed the look with Princess Diana’s sapphire and diamond earrings and the Irish Guards’ gold shamrock brooch, a fitting accessory for her first Trooping as the regiment’s colonel.

Kate Middleton travels by carriage at Trooping the Colour on June 17, 2023. Chris Jackson/Getty Images

The Princess of Wales has attended Trooping the Colour every year since marrying Prince William in 2011, except for 2020 and 2021 when the royal event was scaled down due to the COVID-19 pandemic. The annual birthday parade for the British monarch is organized by the Household Division of the British Army and is one of the most anticipated events on the royal family’s calendar.

Kate’s attendance at Trooping the Colour was confirmed the day ahead of the big event as she released a new photo and personal letter featuring an update on her ongoing cancer treatment.

Kate Middleton arrives at Trooping the Colour on June 15, 2024 alongside Prince George and Princess Charlotte. JUSTIN TALLIS/AFP via Getty

“I’m looking forward to attending the King’s Birthday Parade this weekend with my family and hope to join a few public engagements over the summer, but equally knowing I am not out of the woods yet,” she said in the June 14 letter.

While her Trooping outing marked her first royal engagement since December when she joined the family at their traditional Christmas church visit, it does not signal a full return to royal duties. Princess Kate shared her “hope to join a few public engagements over the summer,” but upcoming appearances will be based on when she feels able and under the guidance of her medical team.

Kate Middleton arrives at Trooping the Colour on June 15, 2024. Alamy

The Princess of Wales acknowledged in her letter, “I am making good progress, but as anyone going through chemotherapy will know, there are good days and bad days. On those bad days, you feel weak, tired and you have to give in to your body resting. But on the good days, when you feel stronger, you want to make the most of feeling well.”

Kate added, “On the days I feel well enough, it is a joy to engage with school life, spend personal time on the things that give me energy and positivity, as well as starting to do a little work from home.”

Kate Middleton in a photo by Matt Porteous released on June 14, 2024. Matt Porteous

Hundreds of soldiers, horses and musicians united for Trooping the Colour, continuing a tradition linked to the monarch’s official birthday since 1748, according to the British Army. The celebration is usually held in June, regardless of when the reigning monarch’s actual birthday may be. (The reason? There’s more likely to be parade-friendly weather!)

Buckingham Palace previously announced that King Charles, 75, would participate in Trooping the Colour in a different way this year amid his cancer treatment. Instead of riding on horseback as he has in years past, including the first Trooping the Colour of his royal reign in June 2023, the King planned to conduct the review from a carriage alongside Queen Camilla.

Kate Middleton arrives at Trooping the Colour on June 15, 2024. Samir Hussein/WireImage

Because only one flag, or “colour,” can be trooped at a time, the five regiments of the Foot Guards — Grenadier, Coldstream, Scots, Irish and Welsh — rotate annually. Princess Kate is the honorary colonel of the Irish Guards, which is presenting its flag this year. However, the Princess of Wales did not lead the Colonel’s Review one week before Trooping and sent a letter expressing her “apologies.”

“I wanted to write and let you know how proud I am of the entire regiment ahead of the Colonel’s Review and Trooping of the Colour,” she said in a message circulated on June 8. “I appreciate everyone trooping this year has been practicing for months and dedicating many hours to ensuring their uniforms and drill are immaculate.”

“Being your colonel remains a great honor, and I am very sorry that I’m unable to take the salute at this year’s Colonel’s Review. Please pass my apologies to the whole Regiment, however, I do hope that I am able to represent you all once again very soon,” she continued. “Please send my very best wishes and good luck to all involved.”

Princess Kate signed her name as “Colonel Catherine” in her own handwriting.