Prince William has built girlfriend Kate Middleton a gym at his royal residence.

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Kate – who officially shares an apartment with her sister Pippa in Chelsea, west London – spends so much time at Clarence House, in central London, that the future king agreed to install some exercise equipment so she can work out in private.

A source said: “Kate has all her things there and asked William and Harry if they would allow her to build a gym. She works out for at least an hour a day and loves to stay slim and toned.

She and Pippa use the gym all the time because it has great equipment and it’s completely private.

“She has even had William and Harry doing crunches and press-ups.”

Meanwhile, William has confirmed he will attend the Lord Mayor’s Sporting Heroes Dinner at London’s Guildhall on Thursday (01.05.08).

He is currently deciding whether to take Kate along, after the couple made a pact to keep their relationship out of the public spotlight. A source said: “There’s a table for the Royal party and William has been invited to bring a guest.”