The Christina on the Coast star, 38, and her husband-to-be made the announcement that they plan to tie the knot from a romantic Mexican getaway at the celeb-favorite resort Montage Los Cabos in Cabo San Lucas, where they celebrated Hall's 41st birthday.
The establishment has seen a number of celebrity guests over the years, including recent exes Scott Disick and Amelia Gray Hamlin. It's also where Haack's ex-husband Tarek El Moussa celebrated his engagement to Selling Sunset's Heather Rae Young last August.
A stay at the five-star beachfront accommodation ranges from $872 a night for a room with a king-size bed, to $13,855 a night for some of the private homes on the property, according to its website.
Hack and Hall celebrated the birthday boy Sunday by the pool, where they were visited by a popsicle cart. Haack posted a clip of them picking out some frozen treats, as the staff wished Hall a happy birthday. "Thank you! How did you know?" he said.
Hall, an Austin-based realtor, opted for a grapefruit and orange popsicle, while his bride-to-be chose the piña colada flavor. "Popsicle hour. Only at @montageloscabos," Haack wrote with the video on her Instagram Story.
Haack later posted a selfie of them enjoying their popsicles, showing off her diamond engagement ring in the photo, though she quickly deleted the image and posted it again with a heart emoji covering up the jewelry.
"Thank you @bennyandthegems - great friend and best jeweler," Haack wrote of jeweler Benny Hayoun on Sunday, posting a better image of the massive emerald-cut ring.
The hotel helped the happy couple celebrate with a romantic touch, decorating the floor of their luxurious bathroom with rose petals that spelled out "love" and their initials inside hearts. "Thank you @montageloscabos for making this weekend so special," Haack wrote with a photo of the display.
Haack also posted a short clip of their gorgeous ocean view, complete with rolling desert hills and palm trees. "That view," she wrote with a starry-eyed emoji.
The Flip or Flop host previously posted a photo of herself and her shirtless fiancé posing on the balcony, with the beach in the background. "Joshua Hall you're a way better view than any view - always," Haack affectionately wrote in the caption.
They later put on their bathing suits and headed down to the water for another sweet photo, as she penned a birthday tribute. "Happy birthday baby. You give me that teenage kinda love vibe and manly protection. It's a combo for a lifetime of happiness + success," she wrote.
"Thank you for reminding me what life and love are like when you put down the technology. I love you Josh," Haack added.
The couple hit the sand once again for a romantic candlelit dinner on the beach, where she finally let her ring shine. Haack announced the engagement with a series of emojis in the caption, including the heart, infinity, lock, key and ring symbols. She also added the ring emoji to her Instagram bio, next to Hall's name.
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Haack was previously married to El Moussa, 40, with whom she shares daughter Taylor, 10, and son Brayden, 6. She also co-parents 2-year-old son Hudson with ex-husband Ant Anstead, 42, with whom her divorce was finalized in June.