The Mentalist is about to introduce another man in Teresa Lisbon's life — but this time it's a man from her past.

The Shield's Kenny Johnson has been tapped to play Greg Taybeck, the high school boyfriend and ex-fiancé of Lisbon (Robin Tunney), TVGuide.com has learned exclusively. When Greg becomes involved in one of the CBI's cases, Lisbon is a bit rattled.

"I think it takes her longer to get to the bottom of the case because it's hard for her to see the thing clearly," creator and executive producer Bruno Heller tells us. "But it's her understanding of him and his character that helps solve the case."

Ultimately, the reunion will give Lisbon a moment to reflect on her life choices. "She ran away [from that relationship] to find a different life," Heller says. "So, she stops and has to reassess her life and look at the paths not taken. Her boyfriend has kids, and she doesn't. So, how does she feel about that?

"It's about when you get to that point in your life where realize, 'You know what? This is the path I'm on. There actually aren't any crossroads ahead where I can take a different path. This is it,'" Heller continues. "The joys and regrets of that is essentially what [this episode] is about."

Besides his work as Lem on The Shield, Johnson has appeared on such shows as Saving Grace and Cold Case. He most recently recurred on Sons of Anarchy and NBC's short-lived Prime Suspect reboot.

The Mentalist returns with fresh episodes on Thursday, April 26 at 10/9c on CBS. Johnson's episode, titled "So Long, and Thanks for All the Red Snapper," is slated to air May 3.