The duke and duchess of Cambridge, Prince William and Kate Middleton, announced last month that they were expecting. The couple has two children, 4-year-old Prince George and 2-year-old Princess Charlotte.
Kensington Palace officials said in a statement that Queen Elizabeth and other family members were "delighted with the news."
Prince William, Duke of Cambridge, Prince George of Cambridge, Princess Charlotte of Cambridge and Catherine, Duchess of Cambridge depart from Hamburg airport on the last day of their official visit to Poland and Germany on July 21, 2017 in Hamburg, Germany. (Photo by Julian Simmonds - Pool/Getty Images)
The duchess, 35, suffered from hyperemesis gravidarum, or severe morning sickness, during her first two pregnancies, and Kensington Palace officials said last month that she was again dealing with the illness through her third pregnancy.