The 23-year-old Modern Family star and Prokop met while auditioning for High School Musical 3: Senior Year in 2009, and were together for five years. The pair co-starred in Disney channel movie Geek Charming in 2011.
Hyland's rep confirmed the breakup to Us Weekly, and a source tells the magazine the split was amicable.
"Sarah's doing fine. It didn't work out," the insider says. "She's young. They decided they would be better off as friends."
Hyland is best known for her role as Haley Dunphy on Modern Family. The actress celebrated with her co-stars at the 2014 Emmy awards on Monday, but did not bring a date. The sitcom won Outstanding Comedy Series, and will return September 24 on ABC.