​Catherine and William's second child due in April

The Duke and Duchess of Cambridge's second baby is due in April, Britain's royal family announced Monday.

While the public now know when Prince George will have a sibling, the gender of Prince William and Catherine's second baby remains a secret.

As during her first pregnancy, Catherine continues to suffer from hyperemesis gravidarum, the palace said. The condition involves nausea and vomiting more severe than the typical morning sickness many women suffer during early pregnancy.

Catherine's condition meant she was forced to cancel some public engagements and led to the couple announcing her pregnancy September 8 before the usual 12-week milestone. The palace said Monday that her condition had improved.

William and Catherine's first child, Prince George, was born in July 2013.

The second child will become fourth in line to the British throne, regardless of gender.