"I'm going to marry this man!" Duncan tweeted on February 14 along with a photo of herself kissing Tollefson on the cheek.
"Thanks to everyone for the best wishes on mine and @whitneyduncan's engagement," Tollefson tweeted. "I know real original proposing on Valentines day ha."
Duncan also posted a photo of her engagement ring, a band featuring interlocking circles of diamonds, on Facebook and noted her fiance "did good."
Although Duncan, a 28-year-old country singer and former Nashville Star finalist from Nashville, TN, publicly presented herself as single while filmingSurvivor: South Pacific in Summer 2011, she was secretly married when she began an affair with Tollefson during the show.
Duncan had secretly wed Donny Fallgatter, the lead singer for a band called KingBilly, on August 1, 2010 in Gatlinburg, TN, People reported.
Duncan and Fallgatter reportedly announced they had gotten engaged to their friends and family just before Duncan left to film Survivor but hid the fact they were already husband and wife. Duncan then began a relationship withTollefson, her tribemate, while on the island and later revealed her Survivor affair to Fallgatter through an alleged series of phone calls before she returned home.
Following her stint on Survivor, Duncan reportedly moved out of Fallgatter's home. Shortly afterwards, Duncan and Tollefson, 27, were seen together around Nashville and she mentioned a boyfriend in multiple tweets.
A Tennessee judge heard Duncan and Fallgatter's divorce filing on November 8, 2011 and granted it.
In an interview with Reality TV World in December 2011, Duncan said, "I genuinely did fall in love on the island and never in a million years would I have thought that... I would have fallen in love on Survivor."
"I'm not going to start talking about [my marital status] now just because of something that's come out. I don't feel the need to defend myself. I was in an unhealthy and unhappy relationship," she added.