Duchess Kate reportedly suffers from rare medical condition. William is highly concerned for his wife

The Duchess of Cambridge suffers from a rare pregnancy-related disease.

Kate Middleton, who is expecting her third child, is afflicted with hyperemesis gravidarum, as reported by All Cute All The Time.

This rare condition is a type of nausea and vomiting that occurs only during pregnancy. This is worse than the morning sickness and passive nausea commonly experienced by most pregnant women.

Kate has suffered from this during each of her three pregnancies. She experienced severe nausea, fainting, extreme dizziness, and persistent vomiting.

If not addressed, the symptoms can have serious implications. Persistent vomiting can lead to severe dehydration for the mother and the child.

Kate's condition had concerned Prince William so much, especially during her third pregnancy. He had Kate stop her royal outings one month before her due date. Doctors had advised Kate to spend the next weeks getting as much rest as she can.

Kate and William, who have been married for almost seven years, are already parents to two children - Prince George and Princess Charlotte.

They welcomed George on the morning of July 22, 2013. Kate gave birth to Charlotte on May 2, 2015.

During her first pregnancy, Kate was admitted to King Edward VII's Hospital after a bout of severe morning sickness. She was then diagnosed with hyperemesis gravidarum.

Kate's third pregnancy was announced on September 4, 2017. The child is due in April 2018.

Kate and William have been taking George and Charlotte on official visits around the world. The children often take the spotlight from their parents as they capture the crowd's hearts.

George has had adorable encounters with former US President Barack Obama and Canada's Prime Minister Justin Trudeau.

Unconfirmed reports have speculated that William and Kate may try for a fourth child. Kate is said to want to follow in the footsteps of Queen Elizabeth, who have four children.