Max Mumby/Indigo via Getty Images Catherine, Duchess of Cambridge visits the Sunken Garden in the grounds of Kensington Palace on August 30, 2017 in London, England.
William, Kate and Harry have made campaigning about mental health one of their priorities, with both royal brothers saying in recent months how their mother's death in a vehicle crash when they were children had left deep emotional scars.
One of their initiatives that's close to the duchess' heart is Heads Together, a mental health campaign whose aim is to challenge mental health stigma and change how it is perceived.
Middleton had to endure the same complication during her previous pregnancies.
So far, no further royal engagements have been announced for the Duchess of Cambridge and its understood this appearance does not mean she will be resuming full royal duties just yet.
And commenting on the Heads Together campaign he added: "I think it's an extraordinary achievement by this generation of the royal family, they've really done a remarkable thing - no-one would realise if they hadn't done it, which makes it all the more remarkable that they have". "All three of us have seen that mental health is at the heart of so numerous issues we are passionate about".