Celebrity Treasure Island contestant Sam Wallace has hit back at suggestions he is the villain on the show.

Wallace came under fire when he threw fellow contestant Matty McClean under the bus in this week's elimination round.

His attempt to get rid of his biggest competitor backfired, leading to his own teammate - former All Black Zac Guildford - being eliminated instead, prompting some to ask if he'd purposefully got rid of Zac, as another strong competitor.

Unhappy viewers have taken to Twitter to express their frustration at Wallace's gameplay.

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But Wallace has taken to Instagram to hit back, saying: "Before anyone judges me for the way I'm playing @celebritytreasureisland know what I'm playing for!"

He shared a photo of his nephew Beau Charlie in hospital following heart surgery.

The Hits radio host is competing on Treasure Island to win $100,000 for his charity of choice, The Starship Foundation after his nephew had to undergo two heart surgeries at Starship Hospital.

In an earlier Instagram post, Wallace said he was "happy to be a villain fighting for the lives of kids."

Wallace also took the opportunity to poke fun at events in the third episode, including a grudge with fellow contestant Moses Mackay after the two got heated during Tuesday night's challenge.

"To @moses_mackay well played, you were a beast out there! I never hold a grudge, I just got a fright under the water! #cursedcaptain."

In the end, Wallace's team Kahu pipped Mackay's team at the post to win the challenge 3-2.