• Lana Parrilla attends 'Once Upon A Time' Press Line Comic-Con International 2016 at Hilton Bayfront on July 23, 2016 in San Diego, California.

Lana Parrilla attends 'Once Upon A Time' Press Line Comic-Con International 2016 at Hilton Bayfront on July 23, 2016 in San Diego, California. (Photo : Getty Images/Frazer Harrison)

The musical episode of "Once Upon a Time" Season 6 will be the penultimate one. Expected to sing in the episode are Regina Mills (Lana Parrilla), Henry Mills (Jared S. Gilmore), Gepetto (Tony Amendola), Grumpy (Lee Arenberg) and Granny (Beverley Elliott).

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Titled "The Song in Your Heart," the musical episode was directed by Ron Underwood. It is expected that most of the main cast members will be singing and performing more than one song in the episode, which is apparently not a standalone.

Aside from Parrilla and Gilmore, the main cast of "OUAT" Season 6 also includes Ginnifer Goodwin as Snow White/Mary Margaret Blanchard, Jennifer Morrison as Emma Swan, Josh Dallas as Prince Charming/David Bolan, Emilie de Ravin as Belle/Lacey French, Colin O'Donoghue as Captain Hook/Killian Jones, Rebecca Mader as Wicked Witch of the West/Zelena and Robert Carlyle as Rumplestiltskin/Mr. Gold. Among the recurring cast members are Mig Macario as Bashful, Tzi Ma as The Dragon, Sara Tomko as Tiger Lily.

"OUAT" executive producer Edward Kitsis told Entertainment Weekly that the musical episode will be continuing the story. He explained that they are not taking a break from all the intensity just to do a musical.

"We're doing all original songs," Kitsis told the publication. "You're going to see a wide-range of people singing from regulars to cameos to people you wouldn't expect."

Viewers can expect a sing-off between the Evil Queen and the Charmings in the musical episode, TV Line has learned. Aside from furthering what the people behind the ABC fairy tale TV series have been doing, the penultimate episode will set up the finale, according to Kitsis.

Kitsis's fellow "OUAT" executive producer Adam Horowitz also said viewers will probably see more people singing than they had expected. He promised viewers that they will see some fun in how the musical episode was done.

Directed by Steve Pearlman, the "OUAT" Season 6 finale will air on ABC on May 14. The musical episode, which was irected by Ron Underwood, titled "The Song in Your Heart" will air on May 7.

Look back at the cast of "OUAT" in 2015 here: