The Duchess of Cambridge sported a chic Catherine Walker coatdress during the pair's visit to King's College in London.
It was the first time Middleton has been on a solo outing with Her Majesty without another member of the royal family present.
For the occasion, Middleton paired her grey coatdress with a black fascinator and a matching black clutch and heels. She opted for minimal make-up and wore her hair in loose curls.
The Queen, meanwhile, wore a baby pink coat and matching hat for the engagement.
The royal pair were at the college to open Bush House, the latest education and learning facility on the Strand Campus.
They met with students from the Entrepreneurship Institute, which exists to support entrepreneurial thinking, skills, and experience among students and staff.
The last time the pair were seen on an outing together was in 2012, when they were accompanied by Prince Philip to Leicester as part of Her Majesty's Diamond Jubilee tour across the UK.
The event comes after Middletonattended London's Portrait Gala on Tuesday, March 12, where she rewore a floral Alexander McQueen gown.
She also got glammed up for St Patrick's Day celebrations on Sunday. During her visit to the Irish Guards in Hounslow, she wore a $4,000 emerald Alexander McQueen coat.