Kate Winslet Surprise Split

Nothing seemed amiss when a smiling Kate Winslet-a vision of serenity in her Yves Saint Laurent gown-walked down the red carpet solo at this year’s Academy Awards. After all, the actress took home the Oscar last year for her performance in The Reader and was back to present Best Actor to the leading men. “The pressure is certainly off,” she said before the show. “It’s really nice just to be able to relax and enjoy it.”

One week later it would seem that Winslet, 34, had perhaps pulled off the performance of a lifetime. On March 15 she and her director husband, Sam Mendes, 44, announced they had quietly separated earlier this year. After almost seven years of marriage and a son together, Joe, 6 (Winslet also has a daughter, Mia, 9, from her first marriage to British director Jim Threapleton), the split “is entirely amicable and is by mutual agreement,” their attorneys said in a statement, which offered no explanation for the separation. “Both parties are fully committed to the future joint parenting of their children.”

The news came as a sad shock to many who knew Winslet and Mendes. The A-list couple were very “normal” and “non-Hollywood,” says a movie-industry source. “They seemed like they had a solid marriage and relationship. They put as much effort into having a real life as they did on their careers.” Adds another source who has worked with both: “It’s really sad; they just grew apart. It’s tough to be married in this business.”

Winslet first met Mendes, an accomplished director who won an Oscar for 1999’s American Beauty, in 2001 when he wanted to cast her in two plays. “Didn’t want to do the plays, definitely wanted to get his phone number,” she told Vanity Fair in 2008. The two wed in 2003 and split their time between New York City and their country home in England. “If Sam goes away to shoot, we’ll all go too. If I go away to shoot, we all go,” Winslet said in 2004. “It’s very important that we not separate the family.”

That was no problem when Mendes directed his wife in 2008’s Revolutionary Road, a film about a crumbling marriage that reunited the actress with costar Leonardo DiCaprio. Working together, however, may have put strain on their own relationship as Mendes told Britain’s Times last year: “We are very happy, but obviously there is a cathartic aspect of making a movie about a bad marriage.”

The actress even took a hiatus from working after wrapping The Reader to enjoy more quality time with her children. “I’ve had 18 months off, which has been lovely,” she told PEOPLE in February.

Winslet-who was spotted recently vacationing in Mexico without Mendes-gushed about him in her Oscar acceptance speech last year. “I am so lucky to have a wonderful husband and two beautiful children who let me do what I love and who love me just the way that I am,” she said. Remembering such moments leaves friends stunned. Says the movie-industry source: “They seemed so good together. That’s what makes this so surprising.”