Whitney posted images of the newborn as well as pictures of mom and dad both holding him.
"He is everything we've ever dreamed of and more... thank y'all for the prayers. And thank God for such a blessing," Whitney concluded.
Whitney and Keith were able to take their baby home earlier this week, and Whitney wrote on Instagram, "Now the real adventure begins."
Whitney said her water broke when she bent over to tie her shoe last week.
"It's just been #keithney for over 11 years now, but we are about to be parents! TBD on baby boy's arrival #survivorcouple @survivorcbs," Whitney captioned a photo with Keith on September 30 in which she was wearing a hospital gown.
Whitney and Keith got married in Summer 2014 after they competed on The Amazing Race's 25th edition as an "Engaged Couple" earlier that year. (Whitney and Keith were the fourth team eliminated from The Race that season).
"The wedding was supposed to be on June 12 in the Caribbean," Whitney told People in September 2014.
"We had this big destination wedding planned, but then The Amazing Race came along. So we canceled everything and lost a lot of deposits."
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Keith elaborated, "We didn't want to change the wedding, but how often do you get an opportunity like this? We had to do it. Also, I knew we could really compete. The areas where I'm weak, she's strong, and vice versa. And this was a chance to show that we weren't just a showmance; we're a real couple with a real relationship."
Whitney said once the couple returned home from their race around the world, it was "wedding detail hell."
"But it all turned out well and it was a wonderful day," Whitney noted.
"I'm going to marry this man!" Whitney tweeted at the time, along with a photo of herself kissing Keith 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."
Whitney had 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 former Season 5 Nashville Star finalist from Nashville, TN, publicly presented herself as single while filming Survivor: South Pacific in Summer 2011, she was secretly married when she began an affair with Keith during the show.
Whitney had secretly wed Donny Fallgatter, the lead singer for a band called KingBilly, on August 1, 2010 in Gatlinburg, TN, People reported.
Whitney and Donny reportedly announced they had gotten engaged to their friends and family just before the country singer left to filmSurvivor but hid the fact they were already husband and wife.
Whitney then began a relationship with Keith, her tribemate, while filmingSurvivor and later revealed her affair to Donny through an alleged series of phone calls before she returned home.
Following her stint on Survivor, Whitney reportedly moved out of Donny's home. Shortly afterwards, Whitney and Keith were seen together around Nashville and she mentioned a boyfriend in multiple tweets.
A Tennessee judge heard Whitney and Donny's divorce filing in early November 2011 and granted it.
In an interview with Reality TV World in December 2011, Whitney shared, "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 onSurvivor."
"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.