“Living the Beatles Legend: The Untold Story of Mal Evans” — the new biography of the Fab Four’s roadie and personal assistant in their innermost circle — was originally titled “Living the Beatles Legend: Or 200 Miles to Go” on Evans’ own manuscript, slated to be published before his untimely death in 1976.

And the tale behind that is just one of many magical mysteries unraveled in the book.

“The story comes from January 1963,” “Living the Beatles Legend” author Kenneth Womack told The Post. “Please Please Me was about to be their first No. 1 single [in the UK]. This is do or die time. You gotta get down to London, be on all big shows. You know, it’s now or never.”

And when his fellow Beatles roadie Neil Aspinall got the flu, it was up to Evans to literally take them on the road from Liverpool to London during a snowstorm in the midst of the UK’s historic Big Freeze.

“So England was essentially cut off by ice, and Mal drove them down — and Liverpool is 200 miles from London,” said Womack. “On the way back, the windshield cracked and basically exploded. Mal knocked out all the pieces of it, as snow and cold air is flying into the van.

“John Lennon wrapped himself in scarves and put, like, a bag over his face and cut eye holes. And the Beatles got in the back, and they made a Beatle sandwich — all four of them — because they were freezing to death.”

And as they shared “one big big bottle of hooch” — as well as each other’s body heat — they would ask Evans how much farther there was on their journey. And their would-be chauffeur would reply, “200 miles to go, fellas.” And it sort of became their mantra when things would get rough in those Beatle years. That experience really brought the guys and Mal together.”

Evans — the Lilverpudlian who went on late-night runs for everything from pot to socks, and shielded John, Paul, George and Ringo from mobs of fans during the height of Beatlemania — gets his own close-up in his new biography that he was presciently preparing for, before his bosses would become music legends.

“Mal kind of is the Beatles’ first historian,” said Womack. “He realizes something important is going on … because nobody thought rock ‘n’ roll was going to be important in 1963-64. They thought, you know, at best it’d be a couple of years, and then you’d have to go get real jobs.”

But Evans could feel that a milestone moment was happening in music history that generations to come would want to have documented.

“You know, he’s keeping the diaries; he starts to save everything ,” said Womack. “And he would keep lyric sheets, he would keep receipts. One time the van broke down, and he kept the receipt for what happened there. [Beatles manager] Brian Epstein would leave paperwork around that he wanted to throw away and Mal would be like, ‘No, no, no — this could be important.”

While the band’s legendary producer George Martin has long been considered “the fifth Beatle,” Evans was right behind him in importance.

“Mal’s the reason they could stay up to 4 a.m., because he could make another meal or go get an instrument if something broke,” said Womack. “He knew who to wake up in the middle of the night to satisfy their every need. And that allowed them to stay up working on one more great song for “Sgt. Pepper” or “The White Album” or what have you.

“I mean, you gotta have a guy like that, right? Because nobody does it alone. All great artists have people behind them who are their champions.”

And Evans sometimes put his own self at risk to protect every hair on the Beatles’ mop-topped heads.

“We get the back story on a lot of really scary moments,” said Womack of the book. “You know, those tours were not as free and easy as they looked. Mal was having to almost singlehandedly sometimes help keep back the crowds … to get the four Beatles and Brian in their car through a mass of people.”

And with his proximity to the Beatles, who he towered over at 6-foot-3, he was a towering presence in many a photo.

“He was a great photo bomber,” said Womack with a laugh.

“He was so much bigger than everybody else, it wasn’t hard to be a photo bomber. They had such a small entourage that … if there was something important that happened, he was the guy who would see it.”

Even after the Beatles broke up in 1970, Evans would continue to work with John Lennon, George Harrison and Ringo Starr, but relations were strained with Paul McCartney while he was suing his former bandmates. Still, all four Beatles gave their endorsement for Evans to write a book about his fab foray with them before his death

But before the book could be published, Evans’ mental health problems led him to provoke a standoff with the police at his home in Los Angeles that resulted in him being shot to death in 1976.

Now — hot on the heels of the “last” Beatles song “Now and Then” plus the expanded reissues of their “Red” and “Blue” collections — Womack has uncovered some rare Beatles lore six decades after they made their debut.

“Diminishing returns suggests that there will be fewer and fewer [new] stories out there,” he said. “That’s just going to be a fact. But we’re really proud that folks will finally learn the true story — warts and all — of Mal’s life.”