It's the first time the monarch and the Duchess of Cambridge have attended an event without another member of the royal family.
On Tuesday, the royals stepped out to attend the opening of Bush House -- a set of buildings that include lecture halls, teaching rooms and an auditorium -- at King's College London's Strand Campus, marking the pair's first joint outing without another member of the royal family present.
In honor of the momentous occasion, the 37-year-old Duchess of Cambridge wore a grey Catherine Walker coat dress, a black Sylvia Fletcher fascinator and matching Gianvito Rossi heels. The Queen, 92, was colorful as always, opting for a light pink coat by Sterwart Parvin and a matching Rachel Trevor-Morgan hat.
The pair arrived to the university by car, with Kate remaining seated until the Queen exited the vehicle. They continued the outing by greeting staff, academics and others at the university. Queen Elizabeth and Kate also visited the university's roof terrace, where they were treated to panoramic views of London.
Reporter Simon Perry even spotted the women being gifted flowers as they departed the engagement.
Their first solo outing together marks a rare engagement for the two. The last time Queen Elizabeth and Kate stepped out together was in March 2012, when they were joined by Prince Philip for a visit to Leicester, which came as part of the Queen's Diamond Jubilee tour. Kate also reportedly hosted the Queen for a private, one-on-one viewing of her wedding dress prior to her nuptials to Prince William in 2011.
The Duchess of Cambridge waited nearly eight years after joining the royal family to have a public, one-on-one outing with the Queen, but Meghan Markle, the Duchess of Sussex, stepped out with the monarch less than a month after marrying Prince Harry. For their first solo engagement last June, the pair traveled by train to Chesire, where they attended multiple events.
Watch the video below for more royals news.
Prince Harry and Meghan Markle Officially Splitting Royal Households From Prince William and Kate Middleton