The Duke and Duchess of Cambridge are believed to be members, as well as Princess Diana

Kate Middleton and Prince William were previously pictured leaving the Harbour Club in Chelsea together back in 2014. The Duke and Duchess of Cambridge are believed to have been members of the gym at the time, although it's not known whether they still are, while the Duke's late mother Princess Diana was also a member there. The Princess of Wales was photographed leaving the facility several times, and was the first royal to give it a seal of approval.

SEE: 21 hilarious photos of royals doing sport: Kate Middleton, Meghan Markle, Prince Harry, more

Now, the gym costs £1555 joining fee per adult, and a further £325 per month for a full membership (totalling an initial price of £1880), including access to all areas of the gym, and use of tennis racquets. There's also a couples' membership option, which will set you back a £3100 joining fee (£1550 each), and £560 per month (£280 each). Take a look inside.

WATCH: Kate Middleton hits the tennis court with Emma Raducanu

Harbour Club Chelsea pool

The gym boasts three pools – a 25m indoor pool, a 25m adult only indoor pool and a 14m waterfall pool.

MORE: Royals exercising: photos of Kate Middleton, Princess Beatrice, Meghan Markle and more as you've never seen them before

Harbour Club Chelsea spa

There's also a hydrotherapy pool, a sauna, a steam room, several spa treatment rooms, six heated beds lining the pool, and an aromatherapy room.

Harbour Club Chelsea tennis court

Kate Middleton and Prince William's gym has plenty of tennis space, including 12 indoor courts, three Padel courts, and two indoor junior tennis courts, should the Cambridge children Prince George, Princess Charlotte and Prince Louis want to try their hand at the sport. There are also tennis coaches available at the club.

SEE: 9 simple ways Meghan Markle stays fit and healthy

Harbour Club Chelsea gym

The gym itself is equipped with every kind of equipment you can think of: treadmills, cross trainers, spin bikes, pilates machines, TRX stations, stairmaster machines, rowing machines and more.

Blaze is their signature HIIT class, which takes place in a dimly-lit room, and combines cardio, strength and combat training while each participant is hooked up to a heart rate monitor.

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