The 27-year-old tweeted her exciting news, adding a picture of the sparkler that sealed the deal.
Luisa was a runner up in series nine of The Apprentice
"Feeling like the luckiest girl in the world," wrote Luisa, with a series of heart emoticons.
"Thanks for all your lovely messages of congratulations on my engagement," she added in another post. "Loving my @Boodles Ashoka cut ring."
Feeling like the luckiest girl in the world ❤️❤️❤️❤️❤️ pic.twitter.com/1O9d7gJlx5— Luisa Zissman (@TheLuluLife) October 10, 2014
Fine diamond jewellery expert Lewis Malka gave the lowdown on the gorgeous sparkler: "The Ashoka cut is synonymous with Boodles and a very rare cut indeed. In reality, it's a modified emerald cut diamond with facets designed by Boodles themselves. Weighing in at a hefty eight carats, and at a very high spec colour and clarity, I would estimate this stunning ring to be worth £1.5million.
"The highlight for me is the split claws on the band, this maximises the light available to the diamond and shows off the incredible fire you would expect from a diamond of this standard. A beautiful piece of jewellery."
Leah Totton, who beat Luisa to become Lord Alan Sugar's business partner in series nine of The Apprentice tweeted her excitement at her friend's news.
"YAY! Huge congrats & much luv to you both," she wrote.
Luisa's husband-to-be also pulled out all the stops with his romantic decorations as she also posted a photo of a stunning floral display with the caption: "The morning after the night before, on cloud 9.... Now how do I take all these flowers home on the Eurostar?!"
The morning after the night before, on cloud 9.... Now how do I take all these flowers home on the Eurostar?! ❤️💎💍 pic.twitter.com/8rFERmJrIO— Luisa Zissman (@TheLuluLife) October 11, 2014
Luisa, who has a four-year-old daughter called Dixie from her previous marriage, has kept the name of her businessman fiancé under wraps.
The Milton Keynes-born entrepeneur has previously said she will not discuss her personal life with the media, but did tell the Daily Star that she is "very happy in a very lovely relationship at the moment."