The singer cited "irreconcilable differences" and requested that her last name be officially changed back to Simpson.
She also asked that the court not award spousal support.
Lachey, who has hired Los Angeles-based attorney Laura Wasser, was not surprised by the filing, a source close to him tells PEOPLE. "He was hoping for the best, but as time went by, he was prepared for what became inevitable," says the source. "(He and Jessica) hadn't spoken in a couple weeks. I think they have spoken about the actual serving of papers."
Shortly after the break, Simpson's uncle Gary, who spent the holiday with the singer and her extended family, told PEOPLE, "She's going to be okay. I know it must be rough on her, but she's doing good."
Surfacing a few days after Thanksgiving, Simpson betrayed no hint of heartache when she showed up at a tanning salon in Studio City, Calif., – minus her wedding band. "She looked great," an observer at South Beach Tan, told PEOPLE.
Reports that their union was in trouble dogged Lachey, 32, and Simpson, 25, for months before their break-up, beginning with stories following a wild bachelor party attended by Lachey in October 2004. The couple denied those stories, with Simpson telling PEOPLE: "Our relationship is better than it's ever been."
Fred Prouser / Reuters
Speaking to PEOPLE about the couple's third anniversary this October, Lachey seemed as smitten as ever. "I wrote (Jessica) a long letter and hid it in her suitcase and made sure she found it today," he said of his wife who was traveling in Africa at the time. “You make the other person feel special because it's easy to lose track."
But attempts to stay together were not successful. The two camps offer different explanations for what went wrong and when. Simpson's side says she was fed up with her husband's partying ways and his refusal to join her family in Texas for Thanksgiving, and that the pair decided to split after an argument the day before Thanksgiving.
But a source close to Lachey says that following dinner in L.A. on Nov. 22, Simpson blindsided her husband on the car ride home. "She said, ‘I don't know if this is working. I want to file for divorce,'" says the source. "He was shocked."
The pair first met at the Hollywood Christmas Parade in 1998, when Lachey was still a member of the pop group 98 Degrees. He said what really made him fall for Simpson was seeing her perform. "I watched her sing and saw the way people responded," he said at the time.
Within weeks of meeting her, he was telling fellow band members, "I'm going to marry that girl." In February 2002 Lachey chartered a yacht in Hawaii and proposed to Simpson as the sun set on the Pacific.
They married in a lavish ceremony on Oct. 26, 2002, in Austin, Texas. Their new life together – mostly spent at their home in Calabasas, Calif. – was chronicled on MTV's reality series Newlyweds: Nick and Jessica.
But now it’s clear that Simpson and Lachey will need to succeed on separate terms. Both have upcoming solo albums. Since their split, Simpson has been staying at her parents' house in L.A. while Lachey remains at the couple's Calabasas, Calif., home.
NIKKI NELSON / WENN / LANDOV