(CNN) -- Vice President Al Gore and his wife, Tipper, have sent an e-mail to family friends announcing a mutual decision to separate, a longtime family friend told CNN.
"We are announcing today that after a great deal of thought and discussion, we have decided to separate," the message said.
"This is very much a mutual and mutually supportive decision that we have made together following a process of long and careful consideration. We ask for respect for our privacy and that of our family, and we do not intend to comment further."
Gore spokeswoman Kalee Kreider confirmed the authenticity of the e-mail but declined to comment further.
The couple, married for 40 years, has four grown children and three grandchildren.
Al and Tipper Gore's dramatic kiss on the podium of the Democratic National Convention in 2000 was credited for giving him a more human image in his presidential run.
"The sheer carnality of the kiss -- the can't-wait-to-get-back-to-the-hotel-room urgency, the sexual electricity flowing south -- was riveting," Time magazine's Lance Morrow wrote at the time.
CNN senior political analyst Gloria Borger described the kiss as "one of the most memorable moments of the campaign."
"For those of us who have watched political couples over the years, this is sad," Borger said. "They are a real couple."
Since losing the 2000 presidential race, Gore has been active in environmental causes, but he has also pursued business interests.
He co-founded Generation Investment Management, a company that promotes "a new approach to sustainable investing." Gore is also the chairman of Current TV, a cable and satellite television network he co-founded. He also serves as a director for Google and Apple Computer.
His best-selling book about global warming -- "An Inconvenient Truth" -- was the subject of an Oscar-winning documentary.
After leaving Washington and returning to Nashville, Tennessee, Tipper Gore considered but decided against a run for a U.S. Senate seat in her home state in 2002.