London (CNN) Prince George arrived for his first day of school with his father Prince William on Thursday, but illness prevented his mother from joining them.

The Duchess of Cambridge, the former Kate Middleton, is suffering from hyperemesis gravidarum , which involves nausea and vomiting more severe than the typical morning sickness many women suffer during early pregnancy.

On Tuesday it was announced that the royal couple is expecting a third child.

Prince George walks into his new school in south London.

But it was George who took center stage on Thursday. Seemingly unperturbed by his new environment, the young prince, age 4, clutched his father's hand as he made his way into Thomas's Battersea, an independent fee-paying school in south London costing £17,604 ($23,000) a year.

Wearing his navy uniform, George shook hands with the head of the lower school, Helen Haslam, before entering the facility.

Prince George arrives for first day at school pic.twitter.com/NewzUqyzhk — Max Foster (@MaxFosterCNN) September 7, 2017

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