Callen's next trip to Russia will change his life forever.

'NCIS: LA' Season 7: FBI Agent Returns For 'Special Episode', Find Out Who!

The NCIS: Los Angeles agent has spent his entire life chasing down his past. After leads took him from Romania to Russia to his own backyard, six seasons of mysteries will come to an end during "Matryoshka: Part 2."

"While they're in Russia, Callen, Sam and Anna (Bar Paly) craft a plan to break Anna's father and his CIA agent companion out of prison," CBS teased. "Also, Special Agent G. Callen finally learns what the 'G' in his name stands for, and in Los Angeles, Kensi and Deeks take Eric into the field on an assignment, on part two of a special two-part episode."

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The episode's first preview brings Callen (Chris O'Donnell) face-to-face with a mysterious man who appears to hold the key to unlocking the orphan's figurative memory box. Once that lock is sprung, however, G may be swept up in a sea of new questions.

"While he's now discovered his identity, Callen's odyssey isn't over," series creator Shane Brennan told Entertainment Weekly. "In many ways, it's just beginning."

Are you ready for the big reveal? Catch NCIS: LA Mondays at 10 p.m. ET on CBS.