The star was standing in a forest pond for the photo shoot, and in some shots, the back of her frock was undone, exposing her rear end.
"A fourth house taurus sun," the Jennifer's Body lead, 37, vaguely captioned the Instagram post, which sent fans into a frenzy and prompted them to wonder if she and fiancé Machine Gun Kelly overcame their issues after taking some time apart.
"How it’s possible cheat on you WTF!?" one person questioned, despite Fox already clarifying "no third party" was involved in their relationship issues.
"@machinegunkelly is so lucky," declared another one of her social media followers, with a third quipping the rapper, 33, will "be kicking himself" if they aren't back together.
Though the Grammy nominee hadn't commented on the post within the first hour it was up, he did make it clear that he approved of her seductive swimsuit photos.
"If this is what a wild animal looks like, I'd let it maul me," he declared in the comments section of a snap that showed the bikini-clad beauty stretched out on a tree limb.
As OK! reported, the two hit a rough patch this past February, with one insider claiming they had "trust issues." After appearing to take some time apart, they allegedly sought out help via couples therapy, and by April, they were spotted playfully walking on the beach while vacationing.
The mom-of-three has also been by the "Emo Girl" crooner's side overseas this summer, as she was seen in the stage wings at his June 7 Berlin concert.
Never miss a story — sign up for the OK! newsletter to stay up-to-date on the best of what OK! has to offer. It’s gossip too good to wait for!
A separate source told People last month that the New Girl alum "seems much happier" since the pair reconciled — though they're in no rush to tie the knot just yet.
"They have done a lot of work to make their relationship strong again and are back together," the insider spilled. "They are engaged, but are not wedding planning."