"Since arriving in England, Cameron was adamant she would keep up with her strict exercise regime," an insider told Mirror.co.uk.
"Producers secured her membership at the ultra discreet, £3,500-a-year gym – totally unaware Prince Harry was also a member.
"Since first clocking one another and saying hello, they have coincided visits on two further occasions.
"During the second one, they were pounding along on adjacent treadmills and Harry cheekily nudged-up Cameron’s speed dial, suggesting a one kilometer race. Cameron agreed... and won.
"They have become pretty friendly – Harry even invited his new gym buddy out drinking with him and his Sloaney chums."