The marriage seemed an odd political alliance: Schwarzenegger, 63, is a Republican from Austria while Shriver, 55, is a member of the Democratic Kennedy family. President John F. Kennedy was her uncle. Her mother was the founder of the Special Olympics. Her father founded the Peace Corps in the Kennedy administration.
Amid allegations of affairs that threatened to derail Schwarzenegger's political career, he admitted that he "behaved badly" and Shriver stood by him. She later went on television's "Oprah" and denied Kennedy women "always look the other way."
"Well, you know, that ticks me off. I, I am my own woman," Shriver said at the time. "I have not been, quote, 'bred' to look the other way. I look at that man back there in the green room straight on, eyes wide open, and I look at him with an open heart."
Shriver has worked as a correspondent for CBS and NBC News and in recent years was devoted to many social causes, including Alzheimer's disease. Schwarzenegger, a former bodybuilder, made is name in films like "Terminator" and "True Lies." The couple left the governor's mansion in January.
Shriver has moved out of the couple's home in the Brentwood section of Los Angeles. They said they will share custody of the children.
The Los Angeles Times reported this week that the couple had been living different lives for some time.
But Howard Bragman, a Hollywood publicist and an ABC News consultant, said it wasn't so surprising: "People in California know that they were very independent."
"A lot of relationships after 25 years -- the kids get grown, people look and say, 'What do we have in common anymore?' And I suspect that's what happened,'" Bragman said.
Rhode Island clinical psychologist Theresa Rando, who has never treated the Schwarzeneggers, said that while bereavement can often bring couples closer together, it can also "destabilize" a marriage.
"We don't know what the problem is," she said. "But what we do know is that when people have losses of individuals who are anchors in their lives, they have to figure out who I am in the world without these people. It makes for a period of questioning and a time of change."
Separations like these can be times of "growth" or they can be "chaotic," she said. "It depends on a number of factors."
Schwarzenegger has publicly said that he will return to Hollywood and make more movies. Shriver, on the other hand, may return to her career in journalism.
Compounded grief can also have the opposite effect, according to psychologists. And some have suggested that the couple had other marital issues but waited until Schwarzenegger was no longer in politics to separate.
"They might not want to add any more fuel to the fire and place more demands on themselves," said Rando. "With a mother dying, a father who has a serious illness, she was getting pulled in all directions. The kids are old enough to be involved in a lot of things and they were dealing with gubernatorial things. Everyone wanted a piece of her."
"What one could do is put everything on hold," she said. "You only have so much energy to triage, if you will. You compartmentalize and later on, you get back to looking at the marital issues or occupational issues. You put things on a back burner."
Sometimes emotional upheaval can be positive, said Rando, and that may be the eventual case with the Shriver-Schwarzenegger separation.
"Turmoil can be a time for growth," she said. "We can break away from the old ways. The Chinese character for crisis is a two-character word: danger and opportunity. It can be a time to try new things."
Still, said Rando, "We don't know what their story is. It remains to be seen."