It almost sounded like heavy rain.

Rocks had started to tumble down Mont Blanc, the tallest mountain in the Alps, and billionaire mogul Sir Richard Branson and his son, Sam, sought shelter behind a boulder, he wrote on his blog.

Branson said a small rock skipped across his son’s head, “loudly clipping” his helmet on the way down.

“A side of a cliff had broken away from the mountain further up and seconds later huge boulders the size of small cars were bouncing towards us,” he wrote. “Rocks rained down on us from every angle. I am not exaggerating when I say four of our team were seconds away from certain death.”

But the father and son emerged uninjured.

They posted about the dangerous expedition Sunday on social media, saying it was part of the Virgin Strive Challenge, which raises money for charity, according to the website. The father and son had joined several others to climb Mont Blanc, which is the highest peak in Western Europe, and Richard Branson said they were crossing Gouter Couloir, known as the “Gully of Death,” when it happened.

“Throughout all of our challenges,” Branson said on Twitter, “I have never come so terrifyingly close to losing myself, my son and other team mates and it all happened in a matter of seconds.”

Branson, 68, could not immediately be reached for comment by The Washington Post.

A video that Sam Branson posted on Instagram showed small rocks scattering down the mountainside as the father and son seemed to be taking cover. Sam Branson said in the post that some of the rocks were as small as coins but that others were as big as refrigerators.

“Rock!” someone called out in the video.

“Whoa, whoa, whoa, whoa, whoa, whoa, whoa,” another person said off camera, shouting, “guys, guys, get it, get in, under the rocks.”

It seemed that Sam Branson then told his father to “stay still” and to protect his head.

On his blog, the elder Branson said his nephew Noah Devereux watched it all unfold from afar — and thought the Bransons were dead.

My nephew Noah was five minutes ahead and had watched with horror the side of the mountain giving way and although he heard our shouts of ‘take cover’ — he was too far away to see what was happening. For a horrifying moment, when Noah turned to find us, all he saw was a gigantic rock where we should have been. He thought we were dead and broke down completely. Horrible. For a few minutes he thought he’d lost us. But by some miracle we all survived. When we were finally able to struggle to our hut for the night — the tears of relief flowed and there were hugs all round. For a month we had spent every day together. My son Sam and nephew Noah, who are the drivers behind these incredible challenges, made me unbelievably proud every day. They motivated and helped their fellow Strivers to complete every stage we faced, no matter the difficulty. Sam and Noah were determined that Mont Blanc would not defeat us. The next morning, as a team, we set off to conquer that summit.

Devereux told Sky News that he was terrified.

“I was screaming ‘Sam! Sam!’ but we didn’t hear anything back,” he told the news organization. “I saw Sam and Richard’s head appear above the crest of ridge behind me and that’s probably one of the greatest senses of relief I’ve ever experienced in my life — so much so I did have a little cry.”

Branson has been in dangerous situations in the past.

As The Washington Post previously reported, during Hurricane Irma, which ravaged the Caribbean islands in 2017, the Virgin Group founder hid out in his wine cellar on his private island.

“All of the team who stayed on Necker and Moskito during the hurricane are safe and well,” Branson said in a blog post at the time.

“We took shelter from the strongest hurricane ever inside the concrete cellar on Necker and very, very fortunately it held firm. Our thoughts go out to everyone affected by the disaster elsewhere in the [British Virgin Islands], Caribbean and beyond,” he said.

After the recent incident in the Alps, Branson said, “We are lucky to be alive."

“It’s been a fantastic challenge that has seen us cycle, sea kayak, hike and climb 2000km across Europe, to the summit of Mont Blanc, the highest mountain in Western Europe,” he wrote on his blog, noting that the group raised “well over” $1.3 million for the children’s charity Big Change. “We’ve experienced every human emotion at their extremes, but every time we’ve heard that little tempting voice in the back of our heads saying ‘why not call it a day,’ we’ve pushed through together and reminded ourselves why we’re doing this in the first place.”

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