Zelena (Rebecca Mader) and Hades (Greg Germann) could have another chance at love in the next episode of "Once Upon a Time" season 5, but it will come at a steep price.

In the episode titled "Sisters," Hades and Zelena will have a romantic picnic, and he will tell her a secret that will help them live a better life outside the Underworld, but it will have a grave effect on the Storybrooke heroes.

"You deserve more, you deserve the real thing. Once my heart is beating again and I can leave this place for good, that's where I want to take you," Hades tells Zelena in the promo clip.

Fortunately, Zelena's half-sister Regina (Lana Parrilla) overhears their conversation. This prompts Regina to ask their mother Cora (Barbara Hershey) to stop Zelena from pursuing their plans. But Cora will reveal a big secret that will leave a big scar in the relationship of her daughters.

According to the synopsis for the upcoming episode, "Now that Hades and Zelena are reunited, Hades tells Zelena that he wants a future with her outside of the Underworld. All she needs to do is heal his heart with True Love's Kiss so they can leave the Underworld and trap the heroes there for eternity. When Regina overhears of this plan, she enlists Cora's help to find a way to separate Zelena from Hades. However, Cora reveals a family secret that could change Regina and Zelena's lives forever."

The episode will show another sibling rivalry, this one between David (Josh Dallas) and his twin brother James. Based on another sneak peek of the episode, James will not appreciate their reunion because he believes that his brother is stealing his spotlight. Will this cause trouble between the two?

"Once Upon a Time" season 5 episode 19 airs Sunday, April 24, on ABC.