Willa Holland has officially exited return of Nyssa al Ghul and a rebirth (of sorts) of the League of Assassins but set up the circumstances of Thea's departure from the series as well.

The latest episode, "The Thanatos Guild," had Nyssa come back, after last being seen in the Arrow season 5 finale, to inform Thea that the new League were after her. Charged by the deceased Malcolm Merlyn, the Thanatos Guild was looking for a map that only Thea could open. By the end of the episode, it was revealed that the map listed the locations of three other Lazarus Pits. Feeling burdened by her father's legacy, Thea (with Roy Harper in tow) ed Nyssa in leaving Star City to destroy the Pits. While Thea's departure came about suddenly, it's been in the works for a very long time.

Related: Thea’s Departure Should Be The Beginning Of The End for Arrow

In a interview with TV Line, Arrow showrunner Marc Guggenheim confirmed that Thea's exit is permanent. It's an idea that had been bouncing around behind-the-scenes since Arrow season 4, due to Willa Holland's desire to pursue other projects. Guggenheim explained:

"Willa had expressed a desire to reduce her episodic commitment to the show and that was sort of done in sort of conjunction with an indication that it was likely that she wouldn’t want to renew her contract past Season 6. So, we’ve kind of known for a while that this was in the offing. We revisited it with Willa at the beginning of Season 6, and she indicated that she hadn’t changed her mind, that she was still interested in moving on."

Guggenheim went on to talk about Thea's exit and said that they wanted to do the best for Willa Holland and the character, as she's always done right by them. This probably explains why Thea's exit was one of the happier departures for Arrow cast . Typically, actors leave the show after they've been killed off or sent away under less than ideal circumstances. Thea, on the other hand, got to ride off into the sunset with the love of her life, Roy.

However, Roy's presence in Thea's goodbye wasn't always the plan. Guggenheim explained that the Arrow writers always imagined that Roy would be apart of the eventual end of Thea's story, but it was happy accident that Colton Haynes was allowed to return. Guggenheim ran into the actor and Haynes expressed his own desire to return to the series; he was unaware of Holland's impending exit. Naturally, Arrow decided to work Roy's return into Thea's departure. Willa Holland has been with the Arrowverse since the very beginning; she was one of Arrow's original series regulars. With Holland's departure, only Stephen Amell, David Ramsey, and Paul Blackthorne remain as steady and original series regulars.

Thea's send-off does fit rather well into Arrow season 6 as a whole. The whole year has put in a lot of effort into radically changing Oliver Queen's life. He's lost his sister, in a fashion, but he's also gained a son and a wife. This is the right move to take for a series in its impressive sixth season. However, Thea's departure does take the series even further away from its beloved roots. Oliver and the team are a lot different than they were in season 1.

More: Why The CW Should Cancel Arrow

Arrow continues with "Brothers in Arms" on April 5 at 9 pm on The CW.

Source: TV Line