Anika Noni Rose, Taye Diggs in "Private Practice"

*Fans of ABC’s “Private Practice” got a glimpse of guest star Anika Noni Rose last week when her character Corrine was bailed out of jail by her brother Sam, played by Taye Diggs, after she robbed a convenience store.

Despite what the promos lead you to believe, she’s not just some drugged out, desperate woman, notes TV Guide. She’s actually mentally ill.

“She’s bipolar,” Rose tells TVGuide.com. “She doesn’t know she’s bipolar, she’s been misdiagnosed many times. No one actually knows what her deal is. She’s been drugged for so long and on the streets for so long, and also self-medicating to try to feel better, but it turns out that she is bipolar and they’re trying to find a way to treat her.”

Now that Sam has her in his care, he’ll turn to Sheldon (Brian Benben) to try to figure out exactly what’s wrong with her. “She’s a little skeptical of the diagnosis because she’s been diagnosed before and people have been wrong,” she says. “She’s been given medication before and it hasn’t worked, so that’s difficult, particularly for somebody who’s fighting with a mental illness because the moment you start to feel better, you think you’re better.”

Through this process the siblings will finally be able to reconnect. “They were close at one point, and then estranged; that will be revealed more as the episodes progress,” Diggs says. “They’re trying to make up for lost time and reintroduce themselves to each other.”

Because of their new found connection, Sam will be in denial over his sister’s illness. “With the people that are closest to you, you don’t want to look at the truth,” Diggs says. ‘It’s the situation where it can happen to everybody else but you. In this situation, something obviously is going on with his sister and he just doesn’t want to believe it.”

Kate Walsh, Taye Diggs, and Anika Noni Rose on Private Practice from "Too Much"

Though Addison (Kate Walsh) and Sam are broken up, she’ll be there to support him through this trying time. “She lives right next door, so she sees first-hand what’s happening and transpiring,” Walsh says. “She’s trying to be his friend and be there for him.”

“Private Practice” airs Thursdays at 10 p.m. on ABC. Watch the promo for the Feb. 9 episode below.