The 38-year-old announced her engagement to her boyfriend, Joshua Hall, Monday during their vacation in Mexico.
Haack shared a slideshow of photos on Instagram from her and Hall's candlelit dinner on the beach.
In one photo, Haack's engagement ring can be seen as she and Hall pose for a selfie.
Haack captioned the post with a heart, lock and key, and diamond ring emojis.
Haack also showed off her engagement ring on Instagram Stories, tagging jeweler Benny Hayoun in the caption.
"Thank you @bennyandthegems - great friend and best jeweler," she wrote.
Haack later posted a photo of the resort with a full moon overhead and referred to Hall as her fiance.
FOLLOW REALITY TV WORLD ON THE ALL-NEW GOOGLE NEWS!
Reality TV World is now available on the all-new Google News app and website. Click here to visit our Google News page, and then click FOLLOW to add us as a news source!
"Full moon vibin' with my fiance," she wrote.
Haack and Hall are in Cabo San Lucas to celebrate Hall's birthday. Haack marked the occasion Sunday by posting a tribute to Hall on Instagram.
"Happy birthday baby. You give me that teenage kinda love vibe and manly protection. It's a combo for a lifetime of happiness + success. Thank you for reminding me what life and love are like when you put down the technology. I love you Josh," she wrote.
Haack was previously married to her "Flip or Flop" co-star Tarek El Moussa and has two children, daughter Taylor, 10, and son Brayden, 6, with him.
She was also wed to Ant Anstead and has a son, Hudson, 2, with the British television presenter.
Haack and Anstead finalized their divorce in June.
Anstead went Instagram official with his new girlfriend, actress Renee Zellweger, last week.
Copyright 2021 United Press International, Inc. (UPI). Any reproduction, republication, redistribution and/or modification of any UPI content is expressly prohibited without UPI's prior written consent.