Superstar Jessica Fox has already won a gold medal at the Paris Olympics but her sternest test may be yet to come — taking on her sister Noemie.

Four-time Olympian Jessica, who finally won the kayak slalom on Sunday local time after near misses in her first three Games, has been joined in Paris by Olympic debutant Noemie, with the pair both set to feature in the kayak cross event.

The discipline, which will be making its debut at the Games, features four athletes taking each other on at the same time while also needing competitors to complete a full 360-degree underwater rotation of their kayak.

Speaking before the Games, Jessica said she had tried to test her sister throughout their childhood.

“She’s just so calm that after a while you stop fighting because you’re not getting the response that you’re after,” she said.

“She’s tough — I don’t like going head-to-head in racing with Noemie, she’s a very fierce competitor.

“In training it’s been so great having each other, because we push each other.

“We haven’t had any bad days — there was one day where I charged on me and she wasn’t expecting it. She was a bit annoyed at me.”

A star in her own right, Noemie sealed her spot for the Games in June by winning silver at a qualification tournament in Prague.

She said joining her sister on the team was “amazing”.

“The overriding emotions are definitely pride ... to wear the green and gold finally,” Noemie said.

“It’s not just (Australian uniform) hand-me-downs, which I’ve always appreciated.

“I feel like I bring that fresh blood to (Jessica), for her to see all the firsts is really exciting ... to live the experience together.

“We’ve made great sparring partners and we’ve both pushed each other forward, quite a long way. There’s something special about being able to just lash out on her because I know she’ll forgive me.”

The pair will take on the kayak cross time trial on Friday night, with their results to determine their placings for round one of the event on Saturday.