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"Once Upon A Time" Season 5 is on a very interesting turning point where our Storybrooke heroes are making their way out of the Underworld, but before that, they will find out a major secret about the king of the Underworld, Hades.

CLICK HERE to watch "Once Upon A Time" Season 5 episode 16, "Our Decay," live online. You can CLICK HERE to watch it later online.

In episode 15, we saw how Captain Hook reunited with his brother Liam and the two joined the others in finding the Underworld version of the "Once Upon A Time" book. But the Jones brothers get blackmailed by Hades, who wanted the pages containing details about him, to be removed. In "The Brothers Jones" Hook also discovered that Liam wasn't exactly the righteousness man he thought he was.

It came out that Liam had come in between Hook and Emma, especially when she caught him doing Hades dirty work. The next episode will show why Hades wanted the pages to be removed.

While the upcoming episode will mostly focus on the adventures of Emma, Snow, David, Regina as they make their way out of the Underworld, the synopsis and the trailer of episode 16 also teases to explore the secret behind the romantic relationship between the king of the Underworld and the Wicked Witch.

Yes, Zelena is back, and according to the synopsis of "Our Decay" Rumple will be forced by Hades to bring Zelena, Belle and Baby Hood to the Underworld. It is also hinted that this will not be a happy reunion.

Not only will Zelena and Regina will get into a sibling squabble in the episode, but the most interesting angle that the episode will explore is that of Hades and Zelena's secret relationship in the past.

The promo of the upcoming episode takes viewers into the flashback, which reveals more about Hades and Zelena's romantic past. It shows that Hades was quite interested in Zelena's powerful spell and decided to visit her in Oz with the intentions of striking an alliance, but the two eventually fell in love with each other. Now, in "Our Decay," we will see why the two kept their relationship a secret and how our heroes will find out what the former lovers are hiding.

Meanwhile, it is said that Belle will get to know something about Rumple that will change her life forever. Is it about him being the Dark One? Will he come clean about it? Will he tell Belle that truth behind the deal he made for his second child? We will have to wait and watch.

Plot synopsis of "Our Decay" (via TV.com) reads: "Hades forces Gold to bring Zelena, Belle and Robin's child to Underbrooke. Zelena and Regina square off, while Belle learns what Gold has been doing in the Underworld. In the past, Hades pays a visit to Oz and becomes romantically involved with Zelena."

"Once Upon A Time" Season 5 episode 16, titled "Our Decay," will be aired on ABC Sunday, April 3, 2016 at 8 p.m.