Royal baby's due date revealed

• The gender of the Duke and Duchess of Cambridge's second baby is still unknown


• Catherine suffers from the condition hyperemesis gravidarum, the palace says


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


• An online betting company says bettors are placing their odds on baby No. 2 to be a girl

(CNN) -- 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.

"Their Royal Highnesses the Duke and Duchess of Cambridge are delighted to confirm they are expecting a baby in April 2015," a statement on the website of the Prince of Wales said.

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.

Palace: Kate and William expecting

Royals warn: Back off Prince George

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.

Read: William and Catherine warn paparazzi to back off Prince George

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

A change in the law last year granting women the same rights of accession to the throne as men means that if the Duchess of Cambridge's baby is a girl, she would be the next in line to the throne after her brother -- even if more sons follow.

Prince Charles is first in line, followed by William, Prince George and then eventually the new baby. The new child will knock future uncle Prince Harry down to fifth.

Read: Why does the "spare heir" matter?

Ladbrokes, a British online betting company, said Monday that bettors are placing their odds on baby No. 2 to be a girl. The heavy favorite for a name? Elizabeth.