Angelina Jolie and Brad Pitt in "Mr. and Mrs. Smith" Credit: Courtesy Everett Collection

Though he was married to Jennifer Aniston at the time, Brad Pitt couldn't take his eyes off of Angelina Jolie on the set of Mr. & Mrs. Smith in 2004.

"I didn't know much about exactly where Brad was in his personal life. But it was clear he was with his best friend, someone he loves and respects," Jolie told Vogue in January 2007. "And so we were both living, I suppose, very full lives."

Though Pitt denied being unfaithful while married to Aniston, Jolie admitted they shared a strong emotional connection. "I think we were the last two people who were looking for a relationship. I certainly wasn't," she said. "We found this strange friendship and partnership that kind of just suddenly happened. I think a few months in I realized, 'God, I can't wait to get to work.'"

It wasn't until the end of the film shoot that they realized "it might mean something more than we'd earlier allowed ourselves to believe," Jolie told Vogue. They were first photographed as a couple while vacationing with Jolie's son Maddox, then 3, in Kenya.

Months after his divorce from Aniston was finalized, Pitt sought to legally adopt Jolie's two children, Maddox and Zahara. They welcomed their first biological daughter, Shiloh, on May 27, 2006 in Swakopmund, Namibia.

The following year, the couple adopted son Pax from Ho Chi Minh City, Vietnam; the process was finalized on February 21, 2008. "Some of my kids are from countries that have seen conflict," Jolie, a UN Goodwill Ambassador, has said. "I usually just explain to them that there are other families in the world that aren't as fortunate as ours and other kids."

Despite their commitment to one another, marriage wasn't always important to Pitt and his partner. "We're not against it. It just doesn't seem necessary," Jolie once explained to Marie Claire. "He and I have never discussed it in detail, but I would assume - because we both went down that road before -- it's not that contract or that ceremony that makes you feel solid." (The actress was previously married to Jonny Lee Miller and Billy Bob Thornton.)

Though marriage wasn't a priority for the stars, expanding their family was. On July 12, 2008, the globetrotting couple welcomed twins Knox and Vivienne. They sold the first photos of the newborns for a reported $14 million, with the proceeds benefiting the Jolie-Pitt Foundation.

As they settled into family life -- whether it be in France, California or New Orleans -- the couple's careers skyrocketed. Jolie made her directorial debut in 2011 with In the Land of Blood and Honey, while Pitt was nominated for an Academy Award for his role in Moneyball.

By January 2012, Pitt revealed his six children were beginning to pressure him to put a ring on Jolie's finger. "It seems to mean more and more to our kids. We made this declaration some time ago that we weren't going to do it till everyone can. But I don't think we’ll be able to hold out," he told The Hollywood Reporter. "It means so much to my kids, and they ask a lot. And it means something to me, too, to make that kind of commitment."

Later that year, Pitt, 48, caved to his children's demands when he popped the question to his love of seven years. He worked with jeweler Robert Procop to design the bauble, which Jolie, 36, debuted at the Los Angeles County Museum of Art's Chinese Galleries April 11.

For Jolie's father, actor Jon Voight, 73, this is only the beginning of the couple's love story. "I'm very happy for them," he tells Us Weekly.