In the video, Sunday explained, "You know when they say it rains, it pours? Well, it really poured on me today. [My T-shirt] says, 'I survived esophageal & ovarian cancer,' and when did I survive that? Well, I'm going to do it right now."
"Because today I was told that I have both, that esophageal cancer started and traveled to my ovary. It's not a super great thing, of course, and not fun to hear, but I will say that I do know I've already survived cancer once and I will survive it again."
"That is why I'm wearing this shirt and saying right now I survived it," Sunday added.
"I know many people are going through difficult times right now, and I just wanted to reach out to you and say, 'You can survive.' If we stick together and are there for each other, it makes the fight so much easier."
Sunday previously battled breast cancer in 2012 and underwent multiple surgeries as well as chemotherapy and radiation, People reported.
Sunday was declared cancer-free before her stint onSurvivor in 2016, and she went on to last for 35 days in the game and finish the season in seventh place.
Sunday, a Christian who wrote Grit Girl: Power to Survive Inspired by Grace in 2018, told People she will lean on her faith during the challenging times ahead, just as she had done eight years prior.
Sunday also intends to receive all the necessary medical treatments that could help her get better, the magazine reported.
Sunday already informed her children of her diagnosis, and she apparently approached the "difficult" conversation with optimism and a positive outlook.
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"They have seen me already survive," Sunday said, referencing her past cancer battle. "We are a house of faith, we put our hope in God, and we believe in hope."
Sunday was a 45-year-old youth pastor from Ostego, MN, when she competed onSurvivor: Millennials vs. Gen X.
"Having to go home this close to the end is just gut-wrenching because you can see the finish line. I know my family is going to be beyond proud of how I played," Sunday said in her final words.
"I slept in the dirt for 30 days, I did challenges I never would have done, I jumped off things I never would've jumped off of -- I'm honestly leaving so proud of myself and I have no regrets about it."
Sunday felt underestimated in the game ofSurvivor, as many of her fellow castaways dubbed her a goat.
"I felt like I came in with a certain skill set and that was my social game with my ability to connect with the millennials, and I did both of those well," Sunday told Reality TV World in an exclusive December 2016 interview.
"I had good relationships with just about everybody, and I felt like I was able to go back and forth with votes, even with people who weren't necessarily in my alliance. So I felt like I was flexible. I felt like I had good relationships. I had the [Ken McNickle] vote, but one move obviously isn't, you know, it doesn't make a winner."
She continued, "But I had my hand in so many other votes and it just wasn't necessarily shown. So it all depends on whom I would've been sitting with, but I felt like I was likable enough where I could have [presented] a case to the jury."
Sunday also talked to Reality TV World about her casting experience and how her breast-cancer battle might've played a role in CBS and producers' interest in her.
"It was my second time applying. I applied for the first time with my son for Blood vs. Water, and then I applied again. I think that fact that I was a breast cancer survivor played a part in it," Sunday shared.
"And then later, not knowing what the theme was going to be, I think that fact I was a young adult pastor and worked with that [millennials] age group is part of what got me on the show."
In addition, Sunday said she "had a blast" playing the game and "would totally play again."