Inside Sadie Robertson's 'Perfect' (and Surprise!) Engagement on Her Family's Farm

Sadie Robertson knew she wanted to spend the rest of her life with Christian Huff, but his proposal came as a total surprise to the Duck Dynasty star.

Following nine months of dating, Huff, 21, popped the question to Robertson, 22, on her family’s farm in Louisiana on Sunday. The timing was extra special for the lovebirds, who are both celebrating birthdays this week: Huff on Sunday and Robertson on Tuesday.

“I knew that we were getting engaged soon because I knew he had talked to my dad [Willie Robertson] and we had talked about it, but I did not know it was coming at the party. It was the most perfect thing ever!” Robertson tells PEOPLE.

For months, the couple had been planning a large joint birthday party, which Huff decided was the perfect day to pop the question.

“Birthdays are my favorite thing ever. Not just my birthday — everybody’s birthday. For months, literally Christian and I have been planning our birthday party together. It’s just my favorite thing that Christian and I share a birthday week even, so ever since I found this out I was like, ‘Oh, we are going to have the most epic birthday of all time,’ ” she says.

“So we planned this huge day, we invited all of our friends from all over to come. All my friends from Nashville, all his friends from Auburn, his family from Florida — everybody came. We decided we were going to do a giant summer Olympic competition with two big teams. All day long was just so fun. We played games and competed and Christian and I actually were on the winning team, so we got lucky on our birthday. It was just the most fun day ever,” she shares.

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Says Robertson, “Even before the engagement, I looked at everybody and was like, ‘This is the best day of my life!’ It was already going really good.”

After a fun day full of games — and a swim in the pond — with friends and family, Huff asked Robertson to put on her favorite outfit.

“After we had all swam in the pond — we were so gross — Christian looked at me and he was like, ‘Alright, I need you to go do something for me.’ I’m like, ‘Alright.’ He’s like, ‘Go put on your favorite outfit that you’ve ever worn.’ Immediately, I was like, ‘Oh my gosh,’ … And so I run upstairs and my heart is like pounding and I get to my room and my mom and his mom and my sisters were in my room waiting on me. And they said, ‘We’re here to be your helpers to help you get ready.’ And I started crying already and we were all crying; we were so happy. All the girls spent an hour getting ready and we prayed together and we talked about how exciting just everything is,” Robertson recalls.

After getting changed into an off-the-shoulder crop top and matching floor-length white skirt, Robertson walked downstairs to Huff, who had carefully planned out every romantic detail of his proposal.

“From that moment, it was just like the most special engagement ever. He had letters from all of my family and all of his family and my Bronco waiting on me. And so when I got in the car, there were all these letters everywhere and our favorite song was on,” she says.

“Then he drove me out to our farmhouse and there it was set up as you see in the pictures with the chair and the blanket and the little torches and stuff,” says Robertson. “He sat me down in the chair and I thought it was just me and him. I had no idea there were any cameras. He showed me later; they were hidden in the trees. There were two people there and I didn’t even know.”

As soon as Huff asked Robertson to be his bride, the Dancing with the Stars alum was beaming with happiness.

“He proposed to me and of course I was so excited. I literally screamed ‘yes’ and he picked me up and it was absolutely perfect,” she says.

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But the romantic details didn’t stop there!

Huff walked Robertson back to her car, where the pair watched a video that featured photos and memories made throughout their relationship.

Details Robertson, “After that, he had this projector set up — and this is the sweetest thing — he had popcorn, M&Ms and Coke, which are like my three go-tos like if I’m going to go out, I go all out. And he had all of it set up with a projector and we sat in the back of the Bronco and he had made this video of all of our pictures and videos just of us as a couple, so we got to sit there and enjoy our little moment of being just me and him together and our life before we came back to the party.”

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Upon returning back to friends and family, the celebrations continued. “And that’s when everyone just completely freaked out and we just celebrated literally all night long. I don’t think anybody went to bed until like 2 a.m. It was so fun!”

While she appreciated every detail throughout the special day, Robertson loved that Huff incorporated “the things that he knows I feel most loved” by into the proposal.

“So thoughtful and so intentional from every detail,” Robertson says.

“It was the words and the letters — the love letters — the love pictures, all our pictures,” she says. “It was perfect.”