This isn't the first installment of the adventure reality series.
Ant embarked on a trip to the Namibian desert with One Direction’s Liam Payne in a previous edition and the former boy band member revealed he suffered suicidal thoughts as he struggled with fame.
The 27-year-old pop star and dad-of-one also shared his relationship regrets with ex Cheryl Cole with the former army man.
Rebel sent fans into a frenzy when she uploaded a photo of herself standing atop a buggy on the sand, a pink bandana around her face.
"Let’s do this!" she captioned the photo that highlighted her 18kg weight loss.
"Istg if you're gonna be on SAS I'm gonna scream," one fan commented.
"Damn Rebel you are thriving through this year ... it’s inspiring," penned another.
The Aussie star also shared an image of herself and Ant with the caption: “Well I survived day one with @AntMiddleton,” along with an emoji of the Mexican flag. However, the post has since been deleted.
Along with her new show, Rebel also has a new boyfriend - 29-year-old Jacob Busch.
The two were introduced by a friend last year and struck up a romance while Rebel was in Australia and Jacob was across the seas in LA during quarantine. After Rebel landed back in the US, she and her new man reunited in California.
"They are officially boyfriend and girlfriend," a source told PEOPLE.
"He's a gentleman, has very old school manners and treats her well. He is also very health conscious and they've been motivating each other with their health journeys."
Rebel's new boyfriend is also worth around US$100 million, with his family being the founders of the Anheuser-Busch brewing dynasty.