The couple were greeted by UK Health Secretary Matt Hancock as they arrived at the inaugural event, with crowds cheering as they caught a glimpse of the royal couple.
Britain's Duchess of Cambridge took extended leave after giving birth to her third child Prince Louis in April, especially in comparison to her six-week and four-month breaks after welcoming Prince George and Princess Charlotte, respectively.
Both wore outfits we've seen previously, with Prince William choosing a classic black and white suit and Kate choosing a long-sleeved lilac dress by designer Emilia Wickstead, which she wore during her royal tour of Germany in 2017.
Eagle-eyed fans of Kate's style will recognise the frock from her and Prince William's royal tour of Germany and Poland past year.
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The Xbox department is under different leadership now, however, with Phil Spencer taking the top role in early 2014. Clearly, this would provide the studio with some stability and heaps of resources from one of the "Big 3".
Another policy up for discussion is a declaration committing to putting mental health on an equal footing with physical health.
The duke and duchess, along with Prince Harry, have made mental health a cornerstone issue of their public work.
Kate and William also met with Dairo Vargas, a contemporary fine artist from Columbia, who is creating an original piece of art at the summit, inspired by the day's events.
The Duchess of Cambridge demonstrated her arty streak yesterday when she was asked to contribute to a painting. At the summit, William and Kate visited a stand run by the non-profit organisation United for Global Mental Health, where they heard about the work of Dixon Chibanda, who started an initiative in Zimbabwe teaching elderly women the skills to offer therapy sessions on "friendship benches". There are just 12 psychiatrists in a population of 14 million people.