NASHVILLE, Tenn. - Country music star Blake Shelton, one of the judges on the NBC singing competition "The Voice," and fellow country star Miranda Lambert announced the end of their four-year marriage Monday.

"This is not the future we envisioned and it is with heavy heart that we move forward separately," Blake, 39, and Lambert, 31, said in a joint statement. "We are real people, with real lives, with real family, friends and colleagues. Therefore, we kindly ask for privacy and compassion concerning this very personal matter."

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TMZ.com specified that Shelton had filed for divorce some time ago and that an Oklahoma judge was expected to finalize it on Monday. The website said the two had a prenuptial agreement.

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This was Lambert's first marriage and Blake's second, following his 2006 divorce from Kaynette Williams, his wife of three years.

Shelton and Lambert dated for five years before their wedding on May 14, 2011. They first met to perform "You're the Reason God Made Oklahoma" together at the taping of CMT's "100 Greatest Duets" in 2005. "Somethin' just happened," Shelton told Nashville.com of that night. "I think we both knew it." He proposed in May 2010.

"I'm married to my best friend!" two-time Grammy Award-winner Lambert had told Us Weekly after the marriage ceremony. "Looking forward to a lifetime of laughter."

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Shelton had told the magazine, "I wanted to be married to Miranda the day I proposed. Finally, it's official!"