The Duchess of Cambridge has had an "anxious" start to her pregnancy but is well, the Duke of Cambridge has said.
In his first appearance since Monday's announcement, Prince William said "there was not much sleep going on" but the pregnancy was "very good news".
Catherine, 35, is suffering from hyperemesis gravidarum, or severe morning sickness, and had to pull out of an engagement on Monday.
The duke thanked well-wishers at a conference in Oxford on Tuesday.
During a visit to the National Mental Health and Policing Conference, he said: "We need Catherine to get over this first bit and then we can start celebrating.
"It's always a bit anxious to start with, but she's well."
He added: "There's not much sleep going on at the moment."
The duke and duchess have a son, George, who is four, and a daughter, Charlotte, aged two.
With the previous two pregnancies, the couple announced them before the 12-week mark - when most women have their first scan - because of the duchess being unwell with hyperemesis gravidarum.
The condition affects about one in every 200 pregnancies and results in severe nausea and vomiting - with one of the main dangers being dehydration.
Later, the duke and Prince Harry visited a new centre which is offering advice and counselling to families affected by the Grenfell Tower fire.
They are to meet members of the community and volunteers in North Kensington at the Support4Grenfell community hub, close to where the tower block stands.
The brothers were due to be joined by the Duchess of Cambridge, but she was forced to pull out from the engagement because of her severe morning sickness.