NASHVILLE - Al Gore once said his romance with wife Tipper inspired the novel

Love Story

, and the couple shared an uncomfortably long kiss before millions on the stage of the Democratic National Convention.

Now, after a 40-year marriage that survived the near-death of a child and the heartache of losing the disputed 2000 presidential election, the former high school sweethearts are calling it quits.

"After a great deal of thought and discussion, we have decided to separate," the Gores wrote in an e-mail to friends Tuesday. "This is very much a mutual and mutually supportive decision that we have made together."

Gore spokeswoman Kalee Kreider confirmed the statement came from the Gores, but she declined to comment further. The Gores told friends that they "grew apart" after four decades of marriage and that there was no affair involved, according to two longtime close associates and family friends.

The couple had carved out separate lives over time, with the 62-year-old former vice president and Nobel Peace Prize laureate on the road frequently, said the associates, who spoke on condition of anonymity because they were not authorized to speak on the couple's behalf.

"Their lives had gotten more and more separated," one of the friends said.

The couple, who own homes in Nashville and Gore's hometown of Carthage, Tenn., had reportedly purchased an $8.8 million estate in Montecito, Calif., this spring.

Married on May 19, 1970, at the National Cathedral in Washington, the Gores crafted an image of a happy couple during his eight-year stint as vice president in the 1990s and a presidential candidate in 2000. Their warm relationship stood in sharp contrast to the Clinton marriage rocked by Bill Clinton's affair with White House intern Monica Lewinsky, a scandal that hung over Gore's own presidential campaign.

At the time, Gore said his wife was "someone I've loved with my whole heart since the night of my high school senior prom." Then, as if to prove it, he planted that long, awkward kiss on her during the 2000 Democratic presidential convention.

In a speech to the 2004 Democratic convention, Gore said he wanted to thank "with all my heart my children and grandchildren, and especially my beloved partner in life, Tipper."

The Love Story claim came in 1997, when Gore told a reporter he and Tipper were the inspiration for Erich Segal's 1970s best-seller. A surprised Segal said that Gore had inspired one side of his male hero's personality - the one controlled by a domineering father - but had nothing to do with Tipper Gore.

The Gores have four children, Karenna, Kristin, Sarah, and Albert III, all now adults.

After losing the 2000 election, Gore turned his attention to climate change, undertaking a worldwide campaign that led in 2007 to a Nobel Peace Prize and an Oscar for the documentary An Inconvenient Truth.

Gore first ran for president in 1988 at age 39 but drew little support outside the South. A planned bid for the 1992 nomination was put aside after the Gores' 6-year-old son almost died after being hit by a car in 1989.

"It was a very spiritual time for both of us," Tipper Gore, 61, later wrote. "In Al's case, he decided to write a book and not to run for president in 1992."

The book was Earth in the Balance, and Al Gore ended up in the thick of the 1992 campaign anyway, as Bill Clinton's running mate.