The contestant fell for Keith Tollefson while on South Pacific – and married to singer Donny Fallgatter

Whitney Duncan’s Survivor: South Pacific bio says she is 27, resides in Nashville and is a country music singer. Check, check, and check.

Asked to describe herself in three words, she lists: Outgoing, happy and honest. Check, check and … not so much.

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The blonde, who portrays herself as single on the show, and who was runner-up in Country Weekly’s “Hottest Bachelorette” earlier this year, has in fact been married since Aug. 1, 2010, when she secretly wed Donny Fallgatter, 32, in Gatlinburg, Tenn.

Fallgatter, from Bismarck, N.D., is lead singer for the band KingBilly. According to a fellow band member, sparks first flew for the couple when their paths crossed in June 2010 during the CMA Music Festival in Nashville.

“They were good together, and they looked good together,” says the source. “They both fell hard.”

The romance heated up quickly, and Duncan moved into Fallgatter’s home and occasionally traveled and performed with KingBilly while they were on tour. Before Duncan left to compete on Survivor in late May, the couple announced their engagement to family and friends.

“Donny was totally faithful while she was gone,” says a close friend. “He even went to help out at her parents’ house in West Tennessee a couple times.”

At one point before returning home, Duncan phoned Fallgatter, and, as Fallgatter told the friend, “He said she sounded weird, like something was up, and not like she was looking forward to seeing him.” Fallgatter’s suspicions were confirmed in a subsequent call, the friend says, when she confessed that she had developed a relationship with another Survivor contestant, Keith Tollefson.

“Donny sent me a text that said, ‘Whitney got into a Survivor relationship.’ I called him and he was really upset so I went over to his place,” says the friend. “That’s when he told me that she wasn’t his fiancé, but his wife, that they had gotten married the summer before. I was totally shocked.”

On Aug. 20, Duncan Tweeted, “Moving furniture all day … sweeet. I’m gonna be really happy when I get a home one day and never have to move again.”

Since then, she and Tollefson have been spotted around Nashville, and she refers to a BF in her Twitter posts. Tollefson, 26, was voted off Survivor on the Nov. 2 episode, leaving Duncan to fend for herself.