Kate and William's royal baby will be the Prince or Princess of Cambridge
Queen Elizabeth II has bestowed the title of His/Her Royal Highness Prince/Princess of Cambridge on the baby, per St. James's Palace. It follows the queen bestowing the title Duke of Cambridge upon Prince William on his wedding to Kate Middleton in 2011 (she is now formally known as Catherine, Duchess of Cambridge). Any future children the couple have will receive the same title.
The queen is free to bestow titles as she sees fit, as long as they're not already claimed by another member of the British aristocracy.
Kate's due date is Saturday (July 13), and news crews have already set up camp outside the London hospital where the baby will be born. According to the Daily Mail, the queen will be the first person outside the delivery room to know when the baby arrives; William will call her on an encrypted phone to break the news.