Is Tiger Woods is being cheated on by his Olympic skiing champion girlfriend? According to RadarOnline, Lindsey Vonn was recently spotted kissing another man backstage at a recent Jay Z, Justin Timberlake show.

Woods, whose marriage to first wife Elin Nordegren infamously imploded after he was rumored to be having affairs with several women, has been dating the 28-year-old Vonn for nearly a year now and the couple made their budding relationship public earlier this year.

Now comes word Vonn was seen "engaging in a very public and very hot make out session" with an older man while backstage at the Jay Z and Justin Timberlake "Sexyback" concert in Miami on Aug. 16. Radar adds the man is believed to be one of Timberlake's tour backup singers.

According to the website, after the concert had ended Vonn and several female friends made their way backstage where she spotted "a guy she very obviously knew well."

Within seconds, Radar reports Vonn "threw herself into his arms and they started on a long session of deep kissing that went on for several minutes." Vonn, who has recently been in Miami as part of a promotional tour, tweeted later that night "wow that was amazing! Best concert I've ever been to!"

"Lindsey's not a nun," a source told Radar."She's a very physical, very attractive young woman with a very strong athlete's ego. She wants her own fame - not his. Now it looks like she's checking out the playing field."