Remembering Michael Jackson as a father, not just as a superstar. TJ Jackson, Michael's nephew and the guardian of his children, tells Barbara Walters about what the star was like as a parent on Barbara Walters Presents: Michael Jackson: The Man in the Mirror, premiering Tuesday, December 20.

The Investigation Discovery special's preview clip, which is exclusive to Us Weekly, shows the broadcasting legend asking TJ, 38, what he taught Michael Jr., 19, Paris, 18, and Prince, 14.

Walters tells viewers in narration, "Certainly, Michael left behind a musical legacy that is vast and indelible, but he also left behind a personal legacy — his children and his family. In 2012, Michael's nephew TJ formally joined Michael's mother, Katherine, as coguardian of his children."

TJ, a singer whose father is Jackson 5 original member Tito Jackson, explains that Michael had already instilled important values in the children before his June 2009 death

"I don't think there's anything I had to teach them because my uncle taught them everything they need to know," TJ says. "All the important things — their core ethics and values are so strong, and there's moments where I just hear my uncle's voice come out of them because [of] their love for people and their innocence."

As for what he tells Michael's kids about their father, TJ reveals, "I don't even spend time on my uncle with them as a performer. I just try to make sure that they know their father was one of the greatest, greatest fathers. And that's why it's tough for me, because he never got to finish his job as a parent."

Watch the clip above. Barbara Walters Presents: Michael Jackson: The Man in the Mirror airs on Investigation Discovery Tuesday, December 20, at 8 p.m. ET. 

Sign up now for the Us Weekly newsletter to get breaking celebrity news, hot pics and more delivered straight to your inbox!