By John Blake, CNN

C.S. Lewis was talking to his lawyer one day when the attorney told him he had to decide where his earnings would go after his death.

Lewis, who had already written “The Chronicles of Narnia” book series, told the lawyer he didn’t need to worry.

“After I’ve been dead five years, no one will read anything I’ve written,” Lewis said.

Lewis was a gifted writer, but he would have been a lousy estate planner. More than 40 years after his death, the former medieval literature professor has become the Elvis Presley of Christian publishing: His legacy is lucrative and still growing, scholars and book editors say.

The third film adaptation of Lewis’ "Narnia" series, “The Voyage of the Dawn Treader,” was released in theaters worldwide this month. HarperOne publishers also just released “The C.S. Lewis Bible,” a book pairing 600 selections of Lewis’ writings with matching scriptural passages.

Lewis’ books remain strong sellers. His “Mere Christianity” has been on the BookScan Religion Bestseller’s list a record 513 weeks since the list started in 2001. At least 430,000 copies of Lewis’ books have been sold this year alone, HarperOne officials said.

Lewis’ contemporary appeal may strike some as odd at first because he seemed so firmly planted in the past. A scholar at the University of Oxford in England, he wore shabby tweed jackets, smoked a pipe in the pub and was wounded in the trenches of World War I.

But Lewis’ popularity endures because of several reasons: his distinctive writing style, a tragic love affair and a shrewd choice he made early in his career, Lewis scholars say.

Lyle Dorsett, author of “Seeking the Secret Place: The Spiritual Formation of C. S. Lewis,” says Lewis was fearless.

“He didn’t dodge the tough questions,” says Dorsett, who told the story of Lewis’ conversation with his lawyer in “Seeking the Secret Place.” “People find that refreshing.”

Lewis’ shrewd early career move

Lewis is labeled a Christian writer, but he also wrote essays, children’s fiction, literary criticism and science fiction. He even hosted a popular BBC radio show during World War II.

Some scholars say Lewis’ BBC experience, where he had to make points quickly, honed his writing style. Lewis learned how to systematically explain Christianity in clear and catchy language, devoid of religious jargon.

Philip Yancey, an evangelical author, says Lewis developed this gift because he came to Christianity as an outsider. He was an atheist.

“Coming to faith as an atheist, he had an understanding of and sympathy for people who look at faith wistfully but can’t swallow it,” says Yancey, who writes about Lewis in his latest book, “What Good is God.”

Lewis remains popular because his books don’t seem dated, says Mickey Maudlin, HarperOne's project editor for "The C.S. Lewis Bible."

Lewis didn’t write about the doctrinal squabbles dividing Christian groups of his time, Maudlin says.

“He made a strategic decision early in his career to talk about ‘Mere Christianity,’ ’’ Maudlin says. “He never writes about different modes of baptism, different views of communion or anything that separates one church from another.”

The result: Lewis has a big following today among Evangelicals, Roman Catholics, Mormons - even skeptics, Maudlin says.

“C.S. Lewis wasn’t trapped by tribal thinking,” Maudlin says. “He was able to speak to everybody. He felt called by God to be an explainer of the big issues.”

How 'good infection’ converted Lewis

Though Lewis looked like the prototype of the mid-20th century English professor, he was actually an Irishman. He was born as Clive Staples Lewis in 1898 in Belfast. Friends and family called him “Jack.”

Scholars cite two events as the source for Lewis’ early atheism. His mother, Florence, died of cancer when Lewis was 9. And his best friend, Paddy, was killed during World War I. Most of the men in Lewis’ platoon didn’t survive the trenches.

“When he saw the carnage of World War I, he concluded that if God exists, He is a cosmic sadist,” says Dorsett, Lewis’ biographer.

Lewis' conversion to Christianity was gradual. It was prompted by what he later called “good infection” - being drawn to faith unawares through the friends he made and books he read.

One of those friends was J.R.R. Tolkien, a fellow English professor at Oxford best known today as the author of “The Lord of the Rings.”

According to some accounts, Tolkien, a Christian intellectual, helped convert Lewis. He showed Lewis that many of the mythological books he loved to read were Christian allegories.

Lewis, though, would later add that there was something more subtle that led to his conversion.

He called it “joy.”

“Joy” was Lewis' term for a stab of longing that unexpectedly welled up in him during moments of contemplation, such as listening to opera or reading an ancient Norse tale.

In his book, “The Weight of Glory,” Lewis wrote that the yearning he experienced during those moments convinced him there was another existence beyond this world.

“For they are not the thing itself; they are only the scent of a love we have not found, the echo of a tune we have not heard, news from a country we have never visited.”

Lewis’ painful love affair

Lewis could be poetic, but he could also be brutally honest. He demonstrated this in his most searing book, “A Grief Observed.”

In the book, Lewis writes about falling in love - and losing that love. Lewis was a bachelor who lived with his older brother Warnie for much of his life. Then he met Joy Davidman Gresham, a Jewish American writer who was 15 years his junior.

Dorsett says Lewis was both physically and intellectually smitten with Gresham. He says they used to play Scrabble together, using Hebrew, Greek, Latin and German words to fill in the blanks.

“She had a sharp wit and he loved it,” Dorsett says. “She loved to debate and challenge him. They were always having an intellectual tennis match.”

Lewis’ relationship with Gresham would also challenge his faith.

Lewis married Gresham when he was 58. Soon, however, she developed bone cancer. She experienced what seemed to be a miraculous recovery only to fall ill again. Four years after marrying Lewis, she was dead.

Lewis was devastated. He began to question his belief in God:

“Go to Him when your need is desperate, when all other help is vain, and what do you find? A door slammed in your face and a sound of bolting,” he wrote in “A Grief Observed.”

“A Grief Observed” inspired the film, “Shadowlands,” starring Anthony Hopkins and Debra Winger. One of the most moving scenes in the film took place when Lewis’ character embraced Gresham’s grieving son, Douglas, and they both wept unabashedly together.

Douglas Gresham is now 65 with a bristly white beard and a booming baritone. He still holds tightly to his memories of Lewis.

Gresham says there’s one part of Lewis’ personality that movies and scholars often get wrong. Many people think Lewis was a dour Englishman.

“He was full of fun,” Gresham says. “He was always surrounded by people who liked to laugh and drink pints of beer. You could always tell if Jack was in the house. You would hear roars of laughter.”

He was also humble, Gresham says. Lewis spent hours each day answering letters from his admirers.

“Jack was someone who believed that if someone would write him, then the least he could do was give a reply,” Gresham says. “Sometimes people would just show up at the door, and he would never turn them away.”

What would Lewis think of his fame?

Gresham says commentators also often miss the mark on Lewis' friendship with Tolkien.

Lewis and Tolkien were both members of the Inklings, an informal literary group at Oxford that met to swap stories and ale.

In “Shadowlands,” Joy Gresham is portrayed as a party crasher who alienated a stuffy Tolkien. Some scholars have suggested that Lewis and Tolkien’s friendship suffered because of Lewis’ marriage to Gresham.

“Tolkien was a devout Catholic,” says Dorsett, Lewis’ biographer. "He found her quite abrasive.”

Gresham, though, snorts at the suggestion that his mother damaged Lewis’ friendship with Tolkien.

“It never happened,” he says.

Gresham says that when he went to visit Lewis in the hospital during his last days, he saw Tolkien. Tolkien told him he could live with him if anything happened to Lewis, Gresham says.

“Now you don’t do that for someone you’re not fond of,” Gresham says. “He was Jack’s best friend when he died.”

Lewis died at 64 of kidney failure on November 22, 1963, the same day President Kennedy was assassinated. His death was overshadowed by coverage of Kennedy’s death as well as the death of Aldous Huxley, another famous author who died that day.

Lewis, however, grabs his share of headlines today.

Gresham, a retired physiotherapist, spends much of his time talking about Lewis. He’s a producer for the latest "Narnia" film, answers letters from Lewis' fans and has written a biography called “Lenten Lands: My Childhood with Joy Davidman and C.S. Lewis.”

He says he doesn’t get tired of talking about the man some still call “Jack.”

“It gives me great pleasure to introduce him to people who haven’t met him yet,” he says. “I’m an unashamed C.S. Lewis fan.”

And what about Lewis? What would he think of the movie franchise he’s spawned and the Christian icon he’s become?

“I think he’d be embarrassed,” Gresham says quickly. “The thought that he would be idolized by so many people would embarrass him deeply.”