They were the happy exceptions — high school sweethearts whose passionate romance led to a famously stable marriage in a capital perpetually rocked by tawdry scandals and sleazy affairs.

But on Tuesday, less than a month after they marked their 40th wedding anniversary, former Vice President and Nobel Peace Prize laureate Al Gore and his wife, Tipper, announced they were breaking up.

The couple, who have four grown children, disclosed the news in a brief e-mail to friends and supporters. Gore, 62, and his wife, 61, gave no hint of whatever hidden turmoil might have caused their union to crumble.

“We are announcing today that after a great deal of thought and discussion, we have decided to separate,” the e-mail said. “This is very much a mutual and mutually supportive decision that we have made together following a process of long and careful consideration.”

If many Americans were disappointed, longtime friends seemed stunned and saddened. A couple that had lived much of their lives in the public eye apparently had kept their heartbreak quiet.

Donna Brazile, who ran Gore’s failed Democratic presidential campaign in 2000, said she was sending the couple “lots of loving thoughts and loads of prayers. They will get through it because these two people truly love one another.”

A family friend in Nashville, who asked not to be identified because of the sensitivity of the matter, said he was “as surprised as everyone else.”

“They’re pretty private when it comes to their personal lives,” the friend said. “They just managed all these years to do that — to keep private.... When my wife heard the news she said, ‘I’d have lost a lot of money on that bet.’ But what do we know about the pressure of people under the spotlight? Who knows what that does to people?”

A close confidant who said he had spoken recently with both Gores dismissed the inevitable speculation about infidelity.

“There’s nothing to that,” he said. “Nothing whatsoever.”

Henry Howard, the Gores’ next-door neighbor in upscale Arlington, Va., said the couple led busy but often separate lives. He said they rarely seemed to appear together at their Tudor-style home outside Washington.

“Usually one would come at a time,” Howard said. “Tipper was there more over the last couple years, and then Al would come in between trips.”

Gore was vice president to Bill Clinton from 1992 to 2000. His pursed-lips propriety and seemingly rock-steady marriage stood in sharp contrast to a president whose sexual affair with a White House intern led to a national scandal and impeachment.

The couple’s separation also came as a surprise because of the most famous kiss in modern politics.

In 2000, when Gore accepted the Democratic nomination for president at a national convention in Los Angeles, Tipper Gore told the cheering crowd that she fell in love with her husband when they met at a high school dance in 1965. They married five years later.

When she finished speaking, the new nominee pulled his startled spouse into a tight embrace, and they exchanged a lip-locking, three-second smooch that dominated news cycles for days.

One Sunday TV talk show guest prudishly called it “X-rated,” and another declared it “disgusting.” Gore, who often seemed wooden on the campaign trail, insisted he was surprised that his buss caused such a buzz.

“Somebody said, ‘Are you trying to send a message?’ I said, ‘Actually, I was trying to send a message to Tipper,’ ” he told CBS’ “The Early Show.”

Gore’s show of public affection gave his flagging campaign a boost in the polls, especially among women. But the kiss was just a kiss: Gore lost the presidency to George W. Bush after a disputed election.

Their romance also hit the headlines when Gore supposedly claimed they had inspired the 1970 book “Love Story,” which was made into a film. The author, Erich Segal, later said he had partly based a character on Gore, but had not based any on his wife.

The Gores have gone public with some of their previous personal trials. Tipper Gore struggled with clinical depression in the early 1990s after their son, Albert, was hit by a car and nearly died.

In the mid-1980s, she led a campaign to limit access to rap music and other recordings with explicit lyrics or content, drawing ire from many performers. The effort led to the voluntary use of parental advisory stickers on selected releases. During her husband’s vice presidency, Tipper Gore became a fervent advocate for better treatment of those with mental health problems.

Al Gore has devoted himself since leaving public office to campaigning against global warming, which he called a “true planetary emergency.” In 2007, he shared the Nobel Peace Prize with the United Nations Intergovernmental Panel on Climate Change.

The Gores did not say whether they planned to divorce, or whether they would divide their property. This year, the couple spent nearly $8.9 million to buy an Italianate-style ocean-view villa with a swimming pool and fountains on 1.5 acres in Montecito, near Santa Barbara.

In their e-mail, the couple asked for “respect for our privacy and that of our family,” and said they would not comment further.

Kalee Kreider, a spokeswoman for the Gores, said they considered their Nashville home their primary residence. She said she could not comment on whether they both intended to remain in the city.

bob.drogin@latimes.com

kathleen.hennessey@latimes.com