The news comes just months after the couple celebrated their one-year anniversary.
"Madelyn and Chase have broken up. It just wasn't working between them anymore," a source tells ET.
In July, ET spoke with the pair -- who went public with their relationship in June 2020 -- about the second season of their Netflix series, which saw their 16-year-old characters, Sarah and John B, get married. The former couple both supported their characters' marriage, noting that a young age doesn't negate a true love.
"Everybody has their own experience, right? It works for some people," Stokes, 28, said. "We've seen couples who got married at 16 who are now in their 80s and early 90s who are still together and wildly in love. So I don't think that the age should specifically define it. I think love is something that should move that needle."
"Love is love," Cline, 23, noted. "... I also think when you know, you know."
Cline talked more about their relationship last November, telling ET that "love is tight."
"It's cool to share this experience with your favorite people and also your favorite person... I feel very happy," she said, gushing over Stokes and her other Outer Banks co-stars.
While very much in the throws of love at the time, Cline explained that she and Stokes have always been sure to maintain professional "boundaries" while on the set of the Netflix series.
"I think because we were friends before this, we understood how we worked as individuals before we were seeing each other. We knew how we worked professionally and we knew each other's personal boundaries," she said. "... As a rule, we never bring anything negative to set. If there's a disagreement or a conversation that needs to be had that could potentially rain on the parade for that day, that's never something that happens before work."
"When we go to set... we're individuals and we are still, at the very minimum, best friends and we are partners and we are screen partners. We're there to support each other," Cline continued. "Sometimes you give that person space. Sometimes you go and you pull them aside and you talk with them if they had a difficult scene and they need to download or whatever. It's whatever your partner needs at the time."
"I really, really love that and respect that about him and our relationship," she added.
The news of their split comes just months after celebrating their one-year-anniversary in April.
"365 w/ u ❤️," Stokes captioned the cute anniversary post.
With Cline sharing a mushy moment of her own, writing, "Thanks for helping me keep track of my belongings for a whole year (: adore u."
ET has reached out to both Stokes and Cline's reps for comment.