The Duchess of Cambridge is still feeling unwell during her first trimester, canceling another appearance due to severe morning sickness.
Catherine, who is pregnant with her and Britain's Prince William's second child, was expected to appear at the opening of the Clore Art Room at London's Barlby Primary School on Wednesday.
But she had to withdraw from the event as she continues to deal with hyperemesis gravidarum, a severe pregnancy illness from which she also suffered during her pregnancy with her first child, Prince George, palace officials said.
Catherine, 32, has been a patron of the Art Room, a charity that provides art therapy for children, since 2012.
The duchess sent a message of support -- and apology -- to the organization, which is celebrating the Clore Duffield Foundation's 50th anniversary.
"I am truly sorry that I cannot be with you all today as you celebrate this milestone," the message said. "As Patron of the Art Room, I feel great pride to see the work that the charity is doing. Vulnerable children flourish in the safe havens that the Art Room provides; this highlights just how important it is to support children at a time when they most need help and support."
William, the second in line to the British throne, and Catherine announced the duchess' second pregnancy early last month and earlier than expected because her illness hampered her from fulfilling her royal duties. Kate was also scheduled to take her first solo overseas trip to Malta in mid-September but her dutiful husband took the trip to celebrate the island nation's independence instead.