The 35-year-old royal, who has not been seen since August 30, joined Prince William, 35, and Prince Harry, 33, to host an event at Buckingham Palace for mental health workers.
The duchess looked stunning in a powder blue Temperley London dress, which visibly showed a small bump.
Kate has taken six weeks off royal duties after being struck down with the same severe strand of morning sickness that she suffered while pregnant with Prince George, 4, and Princess Charlotte, 2.
An aide revealed tonight that the duchess is still suffering from hyperemesis gravidarum but said her condition is improving.
This article originally appeared on New Idea.