Prince William stunned staff at a pizza restaurant at the Oxford Castle when he dropped in for a meal with his girlfriend.

The Prince, 24, treated girlfriend Kate Middleton to some Italian food and a bottle of Chardonnay at Pizza Express in the £40m complex, which was officially opened by the Queen in May.

The Prince arrived at the restaurant unannounced at 8pm on Saturday and was shown to a table for nine to celebrate a friend's graduation.

William tucked into a £6.95 Fiorentina pizza and chose the house Chardonnay, costing £11.55, as two bodyguards watched from a nearby table. Girlfriend Kate chose a salad nicoise.

Trainee manager Kirsty Kinnear, who was on duty on the night, said: "Staff were very excited but the Prince was very understated, so we just gave him the normal service.

"They sat downstairs very discreetly and we tried to respect their privacy - we didn't take any photos.

"Our waiter Steve Byrne served them and said the Prince was very friendly. He didn't say anything in particular - it was just general chit-chat."

Miss Kinnear said the Royal party were dressed in casual clothes and could have been any group of young people enjoying a night out.

The restaurant said it would consider rewording their menu to rename the pizza he chose - with spinach, mozzarella, and a fried egg topping - the 'Royal Fiorentina'.

A fellow diner said: "Not everyone recognised him and there was no fuss.

"He was just like anyone else in the restaurant and seemed to have a great time."

William and his party skipped dessert and after their 90-minute stay he picked up the bill and thanked the staff for their service on the way out.

The Prince is the latest royal visitor to Oxfordshire. Last month, Princess Anne witnessed bun-throwing in Abingdon as she joined Royal Charter celebrations and Prince Charles visited Oxford to address the annual conference of the Prayer Book Society.

Prince Harry's girlfriend Chelsy Davy, 20, also paid a visit in April - dropping in at an Abingdon hair salon. She visited Philosophy in East Saint Helen Street before accompanying Prince Harry to a ball at Sandhurst.

William also visited in June last year. He and Miss Middleton attended the wedding of their friends, Hugh van Cutsem and Rose Astor, at St John the Baptist Church, in Burford.