The Prince of Wales surprised Radio 1's Greg James by joining the presenter during his 630-mile tandem bike ride challenge.

Breakfast show host Greg is five days into an eight-day trek, travelling 1,000km through England, Wales and Scotland to his final destination in Edinburgh.

He's been joined along the way by a host of famous faces including comedian Joe Lycett and Tour de France winner Geraint Thomas.

During the latest leg, Prince William hopped on the rear saddle, pedalling for about 30 minutes through the South Yorkshire countryside before informing Greg he had already raised more than £1m for Comic Relief.

Speaking after the ride, Greg told fellow Radio 1 hosts Sam MacGregor and Danni Diston he was still processing the surprise.

"I've got so many flies in my mouth because I've been cycling with my mouth wide open. All our jaws are on the floor from how mad that all was," he said.

And he admitted he was nervous when he realised he would be riding with the prince.

"That's the tightest I've grabbed the handlebars for the whole week," he said.

"When he left, I just sat down quietly and thought, 'Fair play, he did not need to do that.'

"But I didn't kill the future king."

Prince William joined Greg just outside Doncaster, and praised the host for his latest charity effort.

"What you've done is set an example about helping out. That's the thing," Prince William told Greg.

"It's volunteering some of your time, putting yourself through a bit of pain at the same time, and supporting others.

"It's something we do very well in this country, but we don't really shout about it enough."

He congratulated everyone working on the challenge for "an amazing team effort".

Earlier this week, the prince sent a letter to Greg to wish him luck as he embarked on his challenge.

The two recently worked together on a special edition of Radio 1's Life Hacks, where they discussed male mental health and male suicide.

He previously completed five triathlons in five days in 2016 before cycling between - and climbing - Scafell Pike, Snowdon and Ben Nevis two years later.

"He knows that and he knows how much it means to me."

The presenter also said his plans might change if his dad's condition changed, but said he was "slowly but surely improving a bit".

Radio 1's Longest Ride with Greg James for Red Nose Day will be broadcast live across Radio 1, as well as on iPlayer and YouTube during his journey.

You can also follow live updates here.

Listen to Newsbeat live at 12:45 and 17:45 weekdays - or listen back here.