Homer and Marge are to separate after more than 25 years together on hit cartoon The Simpsons, its executive producer says.

In a link on the show's Twitter feed on Wednesday, Al Jean said it will emerge at the start of the show's 27th season in September that their relationship has been strained for some time.

"In the premiere, it's discovered after all the years Homer has narcolepsy (a sleep disorder) and it's an incredible strain on the marriage," he told industry journal Variety.

"Homer and Marge legally separate, and Homer falls in love with his pharmacist, who's voiced by (Girls creator and star) Lena Dunham," he added in the comments, published earlier this week.

At the weekend, Entertainment Weekly reported that Homer and Marge's adventure-prone son Bart will be killed during the next season, which premieres on September 27.

Sideshow Bob - Krusty the Clown's evil former sidekick - will finally fulfil his long-held dream of dispatching Bart, it said.

"I (hate) frustration comedy so we'll scratch that itch," Jean told EW.

But fear not: the execution will take place in the annual Halloween episode - which by Simpsons tradition doesn't fit into the usual format of the show, meaning Bart can subsequently be revived.

The Simpsons, which first aired in December 1989, averages 7.7 million viewers on television and online in the United States. Millions more enjoy the show in foreign markets, according to US parent network Fox.

Last month, Fox announced that it had renewed the long-running series for two more seasons.