The former Kate Middleton teamed up with the monarch to visit a new facility at King's College London, the fourth oldest university in England and a world research leader.
King's College is known for its groundbreaking research, including the discovery of DNA and work that led to development of televisions, radar and mobile phones.
The royals greeted crowd members after arriving together on the campus.
The duchess, 37, and the queen, 92, have attended numerous royal events together recently, including one last week commemorating Commonwealth Day. The duchess also attended a Buckingham Palace reception earlier this month recognizing her father-in-law — and the monarch’s oldest child — Prince Charles and the 50th anniversary of his investiture.
However, the two women rarely appear by themselves for official engagements.
That doesn't appear to be a reflection of their relationship, however, as the pair often are seen in public enjoying each other's company.
And not one to play favorites, the queen has previously been joined by the Duchess of Cambridge's sister-in-law, the former Meghan Markle, for a joint engagement as well.