Indeed. When his wife begins labour, Russ jumps in the shower so he can look fresh for the birth photos, something Sparks admits he did when his wife Cathy went into labour with the first of their five children, now aged 15 to 25.

Two By Two features a salad bar of turmoil - illness, death, despair, adultery - but divorce dominates the narrative. (Fear not, the book also contains a love story.) Divorce is something Sparks now knows.

After 25 years of marriage, the laureate of love and Cathy, who long served as his muse, divorced last October, no reason given.

"For our children's sake, we regard this as a private matter," Sparks said when the couple separated in January last year. Fans lamented on Twitter: "There's no hope for any of us."

"The vast majority of the book was written after my divorce," Sparks says. But, he adds: "I wanted to make sure the story felt authentic, the dissolution felt authentic, the pain felt authentic, the achingly slow healing felt authentic. Anyone who's been through anything like this knows the healing is slow."

He hopes, however, that his audience would not confuse his experience with the novel, especially the wife, Vivian, who will win no popularity contests. "Vivian is not Cathy," he says. "We remain friends. Our story is different."

As a gift to his readers, he commissioned an original song for the book by musician J.D. Eicher, whose big break was having a tune selected for an Olive Garden commercial.

Eicher accompanied Sparks on his book tour - singing while fans waited in line to have books signed - and witnessed a proposal at an appearance recently in suburban Denver, a regular Sparks phenomenon.

Two decades after his first tour, the author still appears thrilled to meet his fans, 90 per cent of whom, he estimates, are women. His longest appearance, he recalls, lasted 17 hours: "I think I signed 6,000 books."

There is no formula to his stories. "Each time, I think I'll run out of ideas," he says. "One of the goals is to make each of these novels feel unique. To do that, I vary as much as I conceivably can. I'll vary the theme. I'll vary the ending: happy, bittersweet, tragic.

But he knows what keeps readers happy. "They know there will be a love story and it will be set in North Carolina," he says. "Those are the only two constants."

Ms Theresa Park was a neophyte agent who had never sold a novel when she pulled The Notebook from a stack of unsolicited manuscripts in June 1995.

"The writing was so rough, but two-thirds through, I got choked up, and I'm the least romantic person on the planet," she says.

She recalls thinking: "If this is doing this to me, what's it going to do to the rest of the women of the world?"

Ms Jamie Raab, editor of all 20 books and president of Hachette's Grand Central Publishing, had the same reaction. "I cried and I almost never cry."

She offered US$500,000 to pre-empt an auction. "That's not enough," Ms Park responded. "I was thinking of a lot of money, like Horse Whisperer money."

Ten minutes later, Ms Raab called back and proposed US$1 million.

The three have worked together since.

Sparks, concerned that he might be a one-novel wonder, kept the salesman job for another 15 months after selling The Notebook.

He became a very rich writer, but chose to stay in New Bern, North Carolina, a central coastal town of 30,000.

"It's a quiet life," he says.

Quiet, but hardly simple. Sparks lives in a 2,230 sq m house, with a screening room and a bowling alley, in addition to his writing room, where he plays TV shows in the background while he writes. He bought a Bentley. On his wrist is a Patek Philippe watch that costs five figures. He has more.

Twenty years in, the Nicholas Sparks brand is going full force. The Notebook has been sold to the CW as a TV series.

His agent says she is within "striking distance" of signing a Broadway deal for The Notebook.

After three Sparks movies were released in 18 months, his team decided to hold back the movie rights on Two By Two.

Ms Park says: "It was too much of a glut. We're going to take a little break and give everyone a breather."

WASHINGTON POST