While fans flocked to social media to comment on the star's remarkable transformation, many seemingly missed the subtle "single girl" detail suggesting a break-up.
Jacob, who is worth about US$100 million and whose family are the founders of the Anheuser-Busch brewing dynasty, first went Instagram official with Rebel in September.
Those fans who clued on to the relationship update offered a show of support to Rebel, with one fan writing: "Sounds like it’s time for some restorative alone time. Hang in there, Rebel."
Meanwhile another added: "You may have a lot on your mind, but you look fabulous and glow! Blue and yellow look so great on you! Hope your day gets better and friends spoil you!"
Rebel first shared the news about her journey to better health at the start of 2020, when she pledged she was going to make it her "Year of Health".
"Okay so for me 2020 is going to be called 'The Year of Health' - so I put on the athleisure and went out for a walk," she captioned inspirational photos at the time.
"Deliberately hydrating on the couch right now and trying to avoid the sugar and junk food which is going to be hard after the holidays I’ve just had but I’m going to do it!
"Who’s with me in making some positive changes this year?" she asked fans.
At the time, Rebel proved she was well and truly on her way to achieving her goal, and fans were quick to praise the star for making the positive changes.
“I’m so proud of you!! You look fantastic already with your weight loss,” one said.
“You look great, you look absolutely beautiful beforehand and still now. Such a role model,” penned another.
“You already look amazing! Killing it! Any positive changes are good changes,” a third added.
The pledge came after Rebel proudly wore a figure-hugging blue dress while celebrating on New Year's Eve with royals Zara and Mike Tindall in Sydney, showing off her slimmer curves.
The actress has been training hard since 2019, after hiring celebrity trainer Gunnar Peterson, who revealed she trained at least four times a week.
“When she’s in town, she’s a solid four days a week,” the LA-based fitness expert told US Weekly. “She is such a cool person to work with.”