Whitney Duncan Secretly Married, Now Dating ‘Survivor’ Castmate Keith Tollefson

'Survivor: South Pacific' contestant and country singer Whitney Duncan, who's been flying under the radar for weeks on the show, reportedly has two huge secrets: She is married to KingBilly lead singer Donny Fallgatter, and she may have cheated on him with her 'Survivor' tribemate Keith Tollefson (pictured above with Duncan).

PEOPLE reports that Duncan -- who identifies as single and only first made some noise on this season of 'Survivor' when she lashed out at her castmate Cochran this week -- married Fallgatter in Tennessee on Aug. 1, 2010, after a lightning quick courtship began at CMA Fest earlier that summer. They never publicly disclosed the marriage. In fact, when Duncan headed off to the South Pacific in late May to film the show, she and Fallgatter announced that they were engaged. They didn't even tell friends and family of their union.

A source tells the magazine that Fallgatter "was totally faithful while she was gone," but claims his wife did not return the courtesy. Apparently, when Duncan called her husband before returning home, she didn't sound like herself, and he immediately felt something was up. In a follow-up call, the singer reportedly confessed that she began seeing her Savaii tribesmate Keith Tollefson during the filming.

Duncan's rep has no comment, but it's worth noting she does refer to a "BF" on Twitter and that she has been spotted with Tollefson in Nashville.

Looks like Whitney Duncan saved all the drama for when the cameras shut off.