Jane Fonda and Lily Tomlin have been "so secretive" about plans to have Dolly Parton guest star on their hit comedy Grace and Frankie, according to castmate Brooklyn Decker.

Longtime friends Jane and Lily have been trying to find a gap in Dolly's schedule to stage a reunion of their 1980 movie classic 9 to 5 on their Netflix series ever since the show launched in 2015, but after four seasons, their dreams have yet to come to fruition.

Actress Brooklyn, who portrays Jane's onscreen daughter, admits she and her other co-stars continually pester the acting icons for updates, but they have so far been kept completely in the dark about how the Parton plans are progressing.

"We beg for it (Dolly's cameo) every episode," she tells journalist Allison Kugel. "They're so secretive about it, that I don't know if it is in the works, or if it will ever happen.

"I know that a lot of fans of Jane and Lily have wanted to see Dolly on the show because of 9 to 5. In the first two seasons they wanted to make sure that they fleshed out the show before they brought in what would be the tornado that is Dolly Parton. Now that we are in season four, they are playing it super close to the vest."

Last spring (17), Tomlin insisted she and Fonda hadn't given up hope of securing Parton for a guest appearance.

"We're praying, we're hoping so," she explained on U.S. talk show The View. "Jane and I are really plugging for it and we've finally convinced the management at Netflix. They're very excited; they're very turned on to it."

The legendary trio has since stoked fans' hopes of a Grace and Frankie get-together, after joining forces at the 69th Annual Primetime Emmy Awards in September (17) to serve as guest presenters.

The fourth season of Grace and Frankie was released on streaming service Netflix last week (ends19Jan18).