SIR Mick Jagger's energy secret has been exposed by an Argentine teenager, who stumbled upon THE ROLLING STONES star's secret stash of vitamins. Sexy LULI FERNANDEZ, 18, became one of Jagger's companions when he recently toured South America with his group - and she discovered what keeps Jagger going when she visited the bathroom in his Four Seasons hotel suite in Buenos Aires. She reveals, "I went into his room to go to the toilet. The bathroom was full of cans of all sorts of vitamins." Fernandez insists she didn't get too attached to Jagger, because, at 62, the rocker is old enough to be her grandfather, and, fortunately for her, the Brit had no plans to romance her. She adds, "Mick confided in me that while there were a lot of girls at this party and it was his last night in Buenos Aires, he no longer liked all that. He never tried anything with me."