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The biggest mystery teased since the premiere of Arrow season 4 will get solved in the upcoming episode titled Eleven-Fifty-Nine. In the chapter, the death of a key character that fans have seen in flash forwards during the previous episodes will finally be revealed.

"I think promos have made it clear this is the episode you find out who's in the grave," executive producer Marc Guggenheim, who co-wrote the upcoming episode with Keto Shimizu, said, according to TVLine.

"We started off this year with the promise of a death and when we worked our way through our various creative choices, we realized that the thing that will give us the most pop going into the end of the season, into next season, unfortunately would be... the character they wound up choosing to be revealed in Wednesday's episode," Guggenheim said.

Warning: Potential spoilers

According to IDigital Times, the grave that Oliver Queen (Stephen Amell) and Barry Allen (Grant Gustin) visit (as shown in the previous episodes) is of an Arrow team member. The death could be of Diggle (David Ramsey) or Thea Queen (Willa Holland). In the trailer, Thea is shown fighting Malcolm Merlin (John Barrowman) multiple times, while Diggle is shown having a heated exchange with Oliver about his brother. However, fans will have to watch the episode to know which character gets killed.

In the episode, Merlyn will try to free Damien Darhk (Neal McDonough) from the Iron Heights prison, where he has been languishing for a longtime. Merlyn has turned back to his villainous ways by teaming up with HIVE, while he eyes to take over from Darhk. Oliver and Diggle have learnt about Merlyn's plan and will be looking to stop him.

Meanwhile, Laurel (Katie Cassidy) gets a surprising offer and Team Arrow's superhacker Felicity (Emily Bett Rickards), who has decided to quit the group, has a heart-to-heart talk with Curtis (Echo Kellum).

Arrow season 4 episode 18 will air on the CW on 6 April at 8pm EDT. Click here to watch the episode online.

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Team #Arrow falls apart TOMORROW at 8/7c. Catch up on the latest episode first:

Posted by Arrow on Tuesday, April 5, 2016