Celebrity parents Jon and Kate Gosselin said they planned to divorce.

The co-stars of Jon and Kate Plus 8, who are parents of five-year-old sextuplets and eight-year-old twins, spoke of their decision to separate during Monday's episode of the TLC cable TV reality series. Near the end of the hour-long episode, a title card summed things up in stark terms: It said that on Monday, "legal proceedings were initiated in Pennsylvania to dissolve the 10-year marriage of Jon and Kate Gosselin."

The network had been promising a major on-air decision from the couple, whose increasingly troubled marriage has dominated the series in recent weeks, as well as fuelling a firestorm of tabloid coverage.

"We've been dealing a long time with this," Kate said, speaking of her marital problems and the attendant publicity.

"It's been a hard seven or eight months," Jon said in one of his separate on-camera sessions. "It's been a really hard last four months. This is the hardest episode ever."

The beginning of the programme was taken up with the delivery and assembly of playhouses for the Gosselin kids. "My stomach is churning because I know this is gonna cause a huge fight," Kate told the camera as the installation process began in their yard.

The latter part of the show focused on the couple as they discussed the painful decision they have settled on.

"I just need relief now," Kate said. "I need to turn the page."

Jon described his relationship with Kate as "a total breakdown of everything".