KATE'S EXPECTING: Royal baby mania over the years

Royal baby mania is heating up yet again.

Monday morning the royal family in England announced on Twitter that Kate Middleton, The Duchess of Cambridge, is expecting a little brother or sister for Prince George.

The announcement came after Kate had to miss an appearance with husband Will due to severe morning sickness. The Duchess similarly suffered from the condition, known as hyperemesis gravidarum, during her pregnancy with Prince George. Doctors at Kensington Palace are attending to the mother, who is less than 12 weeks pregnant.

The new baby will be fourth in line to the throne, after big brother George, who is third in line.

Click through the gallery above to see pictures of royal births and babies over the years.