Hilary Duff gets candid about a past fling. The 38-year-old singer opens up in her latest single, "Mature," about a brief, age-gap romance from her younger years.In her latest interview with Vogue, the former teen star dished on penning the pop-rock track, released on Nov. 6 under Atlantic Records, with her husband Matthew Koma and Madison Love. According to Hilary Duff, the single is:"a little conversation that my present self is having with my younger self. The two of us are reflecting on a past experience and sending love to each other. It’s a chuckle, a wink, and a sense of being grateful that we are sure footed in where we landed." View this post on Instagram Instagram PostIn "Mature," Hilary Duff 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, babe"Carefully choosing her words, she admitted that the song is anecdotal."It’s definitely about a brief experience that I had a long, long time ago. It was extremely therapeutic to write about things that a normal conversation doesn’t really give you the opportunity to."She continued:"I was looking back on this relationship and thinking about whether this guy had a habit of dating younger women or whether I was 'special.'" View this post on Instagram Instagram PostHilary Duff also seemed to echo her sentiments shared with the outlet as she commemorated the release of her comeback on Instagram, writing:"'Mature' speaks to my mature self calling my not so mature self on the phone many years ago, and she’s letting her know we landed softly. This was a brief time with a lover that left me with so many questions… It felt like a good place to start. How are we feeling… Mature?"A look back at Hilary Duff and Joel Madden’s age-gap romanceMeanwhile, following the admission, speculations quickly arose that Hilary Duff took inspiration from her past age-gap relationship when she was in her teens.In 2004, 16-year-old Duff dated the Good Charlotte frontman Joel Madden, who was 25 at the time. Their relationship was only confirmed a year later through Duff's mother, Susan, in a June 2005 interview for Seventeen magazine.The couple dated for two years and amicably called it quits in 2006.Months following their split, Madden started dating Nicole Richie, whom he would marry in 2010. The couple shares two kids, Harlow and Sparrow. View this post on Instagram Instagram PostDespite their past, Madden appears to be on good terms with the pop star as he shared Duff's new track on his Instagram Story upon release, showcasing his support.Reports also claim that Duff and Richie are good friends.