Nicole Richie had the sweetest reaction to Hilary Duff’s new track “Mature,” even as fans speculate the lyrics might reference Nicole’s husband, Joel Madden — who Duff dated from 2004 to 2006.

On Nov. 11, The Simple Life alum posted a playful photo on her Instagram Story featuring her and Hilary lying on the grass, both dressed in black, holding hands and laughing. Tagging the “So Yesterday” singer, Nicole joked, “‘Mature’ is not the word I would use to describe us, but regardless, this song is a BOP.”

Her post followed fan chatter that “Mature” was inspired by Hilary’s past relationship with Joel, who is nine years her senior. On the chorus, Hilary — who was 19 when she and the Good Charlotte rocker split — sings, “She looks like she could be your daughter / Like me before I got smarter / When I was flattered to hear you say / You’re so mature for your age.”

After the song dropped, one fan posted on X (formerly Twitter), “So, Hilary Duff fans, ‘Mature’ is about Joel Madden, right?” Another added, “New Hilary Duff being a Joel Madden diss track is WILD.”

While Hilary hasn’t confirmed any direct inspiration, she’s explained that the track comes from a more reflective place. “‘Mature’ is a little conversation my present self is having with my younger self,” she said in a press release. “We’re reflecting on a past experience and sending love to each other. It’s a chuckle, a wink, and gratitude for where we landed.”

And despite their romantic history, there’s no bad blood between Hilary, Joel, or Nicole. In fact, the two couples — Hilary and her husband Matthew Koma, and Nicole and Joel — are close friends and even neighbors.

“We actually hang out all the time,” Hilary shared on Watch What Happens Live in 2023. “I was just in [Nicole’s] driveway honking for her to come drink wine with us the other day.”