Miss Ross, 74, makes a cameo in her son and daughter-in-law’s upcoming E! show, Ashlee + Evan, during a studio session.
“To sing with Evan is really special to me,” Simpson says as the Empire actor tells his mom, “This is the song me and Ashlee have been working on.”
Evan’s sister, black-ish star, Tracee Ellis Ross, also makes a cameo.
“While [Ashlee] was having the baby, we said we were going to do it just us, but then we saw both our parents behind the curtain watching,” he said. “Also, those nurses can’t stop my mom! Like, Diana Ross just walks in.”
The trio has previously worked together, appearing in the 2014 music video for Evan’s song “How to Live Alone.”
“[My mom] comes into the studio and helps me. She’s so good at it, and she’s been doing it so long. And she’s such a perfectionist,” Evan told PEOPLE of the legendary Supremes singer. “Sometimes I’ll be like, ‘Let me have a few practices before she comes in to hear it.’ ”
When it comes to his mom, “a lot of people are like, ‘That’s Diana’s son, what is he going to do?’ There’s always been a lot of pressure,” he said. “But at the same time, you’ve got to do your own thing. I’m pretty positive Ashlee enjoys my singing, at least most of the time. We sing together all the time, we’re so close.”
Ashlee + Evan premieres Sept. 9 on E!.