Well, that's one reason to file divorce papers. Khloe Kardashian filed for divorce from her husband of four years yesterday (Dec. 13), and now rumors are flying that the youngest Kardashian sister is already moving on -- with Rihanna's ex!

Radar Online reports that Kardashian and baseball player Matt Kemp have been getting close for months.

Kardashian and Kemp were snapped together in the VIP section of the Drake concert in Los Angeles on Nov. 25. On Dec. 1, Kardashian and Kemp both went to see John Legend at the Nokia Theater, also in the City of Angels. On Dec. 9, Kardashian and Kemp were both at the Jay-Z concert in LA -- as was Odom. However, sources say Kardashian and Odom didn't interact at all at the star-studded show.

Kemp famously dated Rihanna, but the pair split in 2010. She's since moved on to the likes of Drake and Chris Brown ... and is now living the single life. Maybe Khloe should give it a try, too!