Tonight on RTÉ One, a very special celebrity episode of Ireland's Fittest Family will see four celebs and their families go head to head in Kilruddery’s famous Hell & Back course.

Each of the celebs will be competing to win €10,000 for the charity of their choice, while the runners up will all receive €1,000 euro for their chosen charity.

So, which celebs signed their family up for a televised fitness challenge? 

First up, Big Brother winner and future Dancing with the Stars competitor Brian Dowling who is accompanied by his husband Arthur Gourounlian, his sister Aoife and his cousin Amanda. He will be competing on behalf of the Family Heart Screening Clinic.

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Next on the line-up? RTÉ Sport’s Jacqui Hurley who takes part with her husband Shane, her cousin Eoin and her husband’s cousin David. She will be competing on behalf of CRY – Cardiac Risk in the Young. 

Olympians Rob and Marian Heffernan who take part with their children Cathal & Meghan. This athletic family will compete on behalf of The Rainbow Club for Children with Autism.

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Fair City actor David O’Sullivan, who is joined by his sister Aoife and his two cousins Dennis and Denise, will compete on behalf of Aoibheann's Pink Tie, a group that supports families battling cancer.

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Now, if you think the Fittest Family team will be going easy on the competitors because of their celebrity status, you would be very much mistaken. Brian, Jacqui, Rob, Marian and David (along with their super fit families) will be put through the obstacle course from hell including cliff hanger walls, balance beams, and the infamous eliminator.

Swamp Trek
The race starts with a quick dash to the cliff hanger walls, if you fall here they have to go back to the start of the climb, then they trek through 100meters of energy-zapping bog, next it’s out over a ladder where they face a 110m dash to a high jump into water. From here it’s a swim to the platform, the first two people onto the platform win the race.

Devil’s Creek
The event begins with a test of balance as they make their way across the beams, them pushing them right to the edge the monkey bars over the swamp. They must attempt these 3 times before they move on. Next up it’s a cargo net climb and if that isn’t enough the swamp awaits, the families must wade through 100 meters of swampy murky mud, Collect a log and sprint with it to the finish line.

Eliminator
The eliminator will be more difficult than ever before, the race begins with them climbing down the hay bales and running 360m, then they jump straight into the freezing cold ice baths, after that they face the first 12foot wall over 3 meters high. Then they’ve got to continue up the hill where they face various obstacles including a pyramid climb and a cargo net crawl. After another wall the winners will be the first family standing up on top of the hay bales.

Watch Ireland's Fittest Family: Celebrity Special on Tuesday, 31st December, on RTÉ One at 6.25pm.