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As tradition dictates, Prince William knighted Sir Marcus with a ceremonial sword at the investiture ceremony, which took place at Buckingham Palace.
After the prestigious affair, the Duke of Cambridge, 31, chatted away to the royal doctor, giving him updates on how much George had grown since the doctor first saw him.
The Queen's former gynaecologist later revealed that helping bring Prince George into the world was a "lovely experience".
Sir Marcus delivered baby George in July of last year, at the exclusive Lindo Wing of St Mary's Hospital in London.
The retired doctor, 71, was also on hand to look after Kate when she suffered from hyperemesis gravidarum at the beginning of her pregnancy. George was the third royal baby that the doctor had delivered, after the Countess of Wessex's two children Lady Louise Windsor and James, Viscount Severn.
After serving as the Queen's surgeon-gynaecologist for two decades, Sir Marcus retired earlier this month. He had worked for the NHS until 2008 but then started practising privately and in a royal capacity.
Sir Marcus has joked that he may be persuaded to return to work to deliver any other babies that William and Kate might be planning.
The Royal Victorian Order is given to people who have served the Queen or her monarchy in a personal way, and may include officials of the royal household, family members or British ambassadors who have helped organise a state visit abroad.
This award is a personal gift from the monarch made independently of 10 Downing Street.