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Radio 1 presenter Nick Grimshaw is set to climb the tallest dunes in the world for Sport Relief, after taking a day off with heat exhaustion.

Nick sat out of Tuesday's The Heat Is On challenge after advice from medics, and told Radio 1 he was feeling "fighting fit".

In an Instagram video he says his body temperature had reached 40 degrees at the end of Monday's event.

Nick said: "It was really scary. It was horrible."

He's travelling across the Namib desert in Namibia, alongside other celebrities like Frankie Bridge and Rob Rinder to raise money for mental health services.

The challenge, which started on Monday, will see them cross the desert by walking, cycling and skiing.

Nick says he "felt great" when they set off, but as soon as he was stopped by a medic for a temperature check just two kilometres before the finish line, he felt "really, really bad".

"It was horrible, I've never experienced that before."

The presenter was told he couldn't finish the day's challenge, and had to take time out to recover.

He saw doctors and received treatment for heat exhaustion, but said not being able to participate was "really hard to deal with".

The challenge lasts over four days, and ends at a shipwreck on the Skeleton Coast of Namibia.

It was originally supposed to be in the freezing temperatures of Mongolia, but was moved to Namibia because of Coronavirus fears.

Nick says he hopes he will be on "top form, ready to continue" to the next stage.

The celebrities are set to climb the "highest sand dunes in the world" which Nick says he doesn't want to miss.

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