This wardrobe staple has come to illustrate her development into a more “involved working royal,” fashion and monarchy expert Christine Ross has told Newsweek.

Kate and William are in Boston on a three-day-trip to attend the second annual Earthshot Prize awards ceremony being held on Friday.

The prize, set up to fund global eco-initiatives, has been spearheaded by William, who took direct inspiration from President John F. Kennedy’s 1962 “moonshot” speech when coming up with the name.

The city was chosen to host the awards ceremony in honor of Kennedy, whose family come from the Boston area.

After a three-outfit day when she first arrived in Boston on Wednesday, Kate cut the number down to two for her public engagements on the second day of the trip.

For their first engagement, Kate and William paid a visit to Greentown Labs in Somerville, Massachusetts, a community of pioneers working on developments in climate technology.

For this event, Kate wore a striking plum-colored pantsuit comprising a sharply tailored blazer with high pocket details and a pair of trumpet-leg pants.

The creator of the suit was later identified as Roland Mouret, a London-based French fashion designer who was responsible for making the black-and-white evening gown worn by the royal to the U.K. premiere of the movie Top Gun: Maverick in May 2022 in London.

The outfit marked the second pantsuit of the trip so far for Kate, who wore a deep purple Alexander McQueen variation on the style for her arrival at Logan International Airport on Wednesday. The McQueen suit is one of Kate’s favorite styles, and she owns it in three other colors, all worn in 2022.

Before, Kate rarely wore pantsuits, and this new style of dressing can be linked to the princess’ new, more-involved role within the royal family, according to Ross.

“We’ve seen a huge shift in the Princess of Wales’s work and presence within the royal family, from cutting ribbons to funding and supporting early childhood development research,” Ross told Newsweek.

“The ascent into pantsuits seems to follow her development into a very-involved working royal. We often see these pantsuits on more business-formal events, where her outfit may fit in better with the people she is meeting.”

Mouret, as a designer, has featured in the royal’s wardrobe for a number of years. In October, he described his most-famous client to The Sunday Times as someone who: “represents the way a woman grows, the way a woman stands not behind but beside. That sense of equality she has created—she’s powerful.”

“Kate has been wearing Roland Mouret for years, a French designer known for his clean lines and structural details,” said Ross.

“Some of Kate’s most-striking and modern eveningwear looks have come from the designer. Roland Mouret’s looks rely on expert tailoring and clean lines, which are sartorial features that Kate always appreciates. Meghan, the duchess of Sussex, counts Mouret as a friend, and also wears his structural and elegant designs.”

Later in the day, William and Kate visited Piers Park at Boston Harbor where they met with representatives of environmental organizations serving the area.

For this outdoor engagement, the prince and princess wrapped up warm in overcoats. Kate selected a layered brown-tone ensemble, with the standout piece being a longline brown coat from Alexander McQueen, a fashion house with whom the royal has a special relationship.

The house, and in particular, its chief designer Sarah Burton, have designed pieces for Kate throughout her married life, including her most-important fashion commission to date—her wedding dress.

“Sarah Burton for Alexander McQueen will become to Kate who Angela Kelly was to Queen Elizabeth II,” Ross said of the late monarch’s dresser and right-hand woman.

“If Kate wants something specific or special, she always looks to the iconic British brand and designer at McQueen. The princess and Burton must have a deeply trusting relationship, as the McQueen styles that Kate wears are almost always fashion hits and become some of her most-memorable looks.

“It certainly promotes the British brand abroad, but more becomes part of Kate’s public identify: McQueen is to Kate what tea is to England.”

The visit concludes on Friday with the Earthshot Prize awards ceremony, giving royal watchers a chance to see Kate dressed in full glamor mode. Those hoping to see a brand-new gown on the princess, though, may be disappointed.

In-line with the Earthshot Prize’s eco-credentials, for the 2021 ceremony, Kate rewore a 10-year-old dress last seen on a visit to Hollywood in 2011.

“The newly titled Princess of Wales has crafted a beautiful wardrobe on her first overseas visit in her new role within the royal family,” Ross said.

“While this isn’t an official tour, it is an opportunity to showcase their royal brand abroad. Kate’s outfits have all featured brand-new designs from her favorite fashion houses, showcasing how Kate hopes to be seen in her role as Princess of Wales.”

Do you have a question about King Charles III, William and Kate, Meghan and Harry or their family that you would like our experienced royal correspondents to answer? Email royals@newsweek.com. We’d love to hear from you.