"My fondest memory with Michael, we were both 14 years old, and it was right after the first American Music Awards; we presented an award," Donny tells ET. "And we thought, 'We're hungry!' So we hopped in the back of my limo, drove to Jack-in-the-Box, and we were sticking our heads out the moon roof eating tacos and driving down Sunset Blvd. We were both laughing our heads off."
"It's still hard for me to imagine a year after his death that he's still gone, that Michael isn't with us," Donny adds. "But his music lives on. Michael will always be with us."
Of course, Donny, a father of five with grandchildren, often thinks of Michael's children, who are now in the care of their grandmother Katherine Jackson.
"She is such a loving woman. I've known her a long, long time. Anytime a child can be raised by grandma, you can't go wrong," he says.
Donny's family is still grieving their own loss, that of Marie's son, Michael. But Marie is healing, he says, with more shows ahead in Las Vegas.
"I went to Yellowstone National Park with my family and she went to China, of all places. Her son is doing a play over there. But she's doing great, I'm doing great -- we can hardly wait to get started up in Las Vegas!" he tells ET.
For now, Donny is busy working with a new co-star -- Mickey Mouse! -- and we were behind the scenes as he filmed a commercial for "Dance Star Mickey," one of the hottest toys from Fisher-Price for the upcoming holidays.
Watch the video for more with Donny.