Usain Bolt may have to explain the way he rang in his birthday.

The Jamaican sprinter celebrated his 30th birthday on Sunday and part of ushering in his new age included some full-on partying and grinding in Brazil. The only issue is the person he was grinding with wasn't exactly his girlfriend.

Bolt has many reasons to celebrate. His birthday capped off the end of an amazing Olympic career for the sprinter. Bolt took home three gold medals at the Summer Games in Rio de Janeiro this summer, placing first in the men's 4x100 meter relay, men's 200 meters and men's 100 meters.

He now has nine Olympic gold medals, adding to the ones he picked up in Beijing (2008) and London (2012).

During his birthday celebration, Bolt was seen grinding with a mystery female partner who was not his girlfriend, Kasi Bennett, according to TMZ Sports. The two parties were hot and heavy as Rihanna's song "Work" blared in the background and the act was caught on video.

It seemed everything was fine between Bolt and Bennett as recently as last week as she bragged about her boyfriend's accomplishments on Instagram. Bolt even referred to her as his "first lady" on social media, however she was nowhere to be found during his birthday party.

Bolt was seen making out with Bennett at a parade in Jamaica back in April, which was around the same time he revealed his love for Rihanna.

"She's giving me no love bro," Bolt told TMZ Sports at the time. "No love. Zero love. There's no competition for me, man. I'm tall, I'm handsome [and] I'm dark. I'm the greatest man. I'm gonna talk to my team, my team is weighing me down. It should have happened already."

He then referred to Bennett being in his life, but he didn't refer to her by name.

"I do have a girlfriend," Bolt confessed. "So ..."

Apparently that fact didn't matter on his 30th birthday.

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