It is unclear how long the couple dated.
"They're still friends, and it's totally mutual," an insider told the magazine's Web site about the split. "They will still talk and see each other. ... Adam is crazy busy right now getting the album done and squeezing in rehearsals. ... They both felt this moment is too important for Adam to focus on anything else but getting this album out and having it be a huge hit."
Lambert's first album "For Your Entertainment" is set for release Nov. 23.
2014: The Year in Music [PHOTOS]