"He was always perfect for me but it was almost so easy that it was like, 'Why is he so perfect for me?' You know what I mean? You almost want to dig for more just to see if it's gonna be harder, like if it's gonna be a chase, but (with Siegfried), I didn't want to ever say goodbye to him, and that's when I knew he's the one."
Both before the cameras and in person, Siegfried, also 27, doesn't seem troubled that Hartsock also had feelings for another guy so soon before they became engaged.
"I just stayed true to how I felt for her and how I felt about the process. . . . I just did a really good job compartmentalizing everything."
The couple said they had to talk to members of his family and reassure them that they are happy together.
"It was maybe a little hard at first but they knew the outcome," Hartsock said.
"She's talked with my mom and she's talked with my family," added Siegfried.
Hartsock's last reality TV romance ended in heartbreak. The bridal stylist competed for the affection of Sean Lowe on "The Bachelor," but was sent home after a disastrous date.
She's moving from Los Angeles to Seattle to be with Siegfried, and although they want an "intimate" wedding when the time is right, they're not ruling out the idea of televising their nuptials like some former "Bachelor" and "Bachelorette" couples have done.
"Next summer, we'll decide if that's something we see fit," said Siegfried.