Katie entered The Bachelorette process hell-bent on getting engaged at the Final Rose Ceremony, but Blake joined Season 17 a few weeks late and the pair essentially played a game of catch-up until Katie realized during her Fantasy Suite with Blake that he's The One.
"I truly actually did not think he was going to propose," Katie revealed during a recent appearance on Good Morning America.
"And so when he actually got down on one knee and proposed, my reaction is actual shock."
Katie confessed to doing a little investigating at the Final Rose Ceremony, as she was in search of a clue Blake may or may not ask for her hand in marriage.
"That day, he had tight pants on, and I looked at the pockets and there was no box," Katie recalled.
"I was like, 'Oh no!' And so when he said the line, 'I can't give you what you came here for,' I was just trying to, like, not give away that I was so sad."
Blake, however, was keeping the ring in his back pocket, and Katie joked, "They were too tight in the front [for a ring box]."
Blake's proposal went off without a hitch, but he seemed hesitant or reluctant to propose marriage when picking out the oval Neil Lane diamond engagement ring currently on Katie's finger.
Blake confirmed he was "freaking out" earlier that day in New Mexico, knowing he was about to pop the question to the love of his life.
But something about Katie gave Blake the confidence to show up on her The Bachelorette season late, possibly face rejection on national television, and then pour his heart out to her on the last day of their televised journey.
"She just was everything that I thought she was going to be," Blake noted. "She was just bold and confident and made decisions, was decisive, and I was just like, 'It's hot, I love that!'"
But before Katie and Blake could cross the finish line into happily-ever-after, Katie was dumped by her apparent The Bachelorette frontrunner, Greg Grippo, who left the show because Katie had refused to provide him with the validation and reassurance he needed after hometown dates.
When asked how her emotional and seemingly devastating breakup with Greg felt in-person vs. watching it back on TV, Katie explained, "It's day and night different."
"In the moment, you see it, I'm apologizing and I feel bad and I'm confused. And seeing the way that he spoke, I was mad. I was pretty mad," Katie said, adding that it was nice to confront Greg on After the Final Rose because it gave her "the closure [she] needed."
Katie also revealed how she had arrived at the decision to continue on with The Bachelorette process after losing Greg.
"When I really took the time to reflect, like, 'Okay, was Greg my actual person? Would we have worked out, outside of this?' And I think had I been with him watching this all back, I don't know that we'd be sitting on a couch together [still dating]," Katie admitted.
Now that Katie and Blake are able to start the next chapter of their lives in public as a happily-engaged couple, Katie said it feels as though "a weight has been lifted off our shoulders."
"It's been long. It feels like a year, honestly. First thing I'm trying to figure out is, like, what's it like driving together in a car?" Katie said with a laugh. "What's it like getting coffee together?"
Katie and Blake are therefore in no rush to tie the knot, although Katie said she has "no doubt" marriage is in their future.
"At some point, there is certainly a wedding. There's no doubt about that," Katie acknowledged.
The pair both confirmed, however, that neither one of them wants roses at their wedding.
"I don't want to give her another rose!" Blake declared with a big smile.
Katie and Blake also shared on Good Morning America that they're currently in the process of deciding where to live. Katie is getting a new place in San Diego, CA, and Blake has a home in Canada and so they're going to try to enjoy both homes for the time being.
They plan on figuring things out one day at a time together.
When Blake proposed marriage to Katie on Monday night's The Bachelorette finale, he said being Katie's last man standing felt like a fairy-tale and they had a connection that initially seemed too good to be true.
"I know how great of a wife you're going to be and mother you're going to be. But I know there's things that scare you," Blake told Katie.
"I know that you in the past have talked about how you've had to compromise who you are to make relationships work, and I don't want you to do that. But I can't give you what you came her for."
"Because you deserve a lot more than that. You deserve the world, and I'm excited to support you and be there for you every day moving forward... Will you marry me?"