Star City is going to be a little less full in the coming weeks, as two major characters left Arrow on tonight's episode.

In the last episode of the month, Arrow dropped a number of shocking developments, but possibly the most surprising was the departure of a pair of characters who have been a big part of the show.

Spoilers ahead for tonight's episode of Arrow.

By the end of the episode, both Curtis Holt (Echo Kellum) and the younger version of William Clayton (Jack Moore) left the city and, as far as we can tell, the series.

The bigger departure, especially given the significant role he is playing in the flash-forwards, is likely William, who moved to Central City with his grandparents.

Why? Well, he just wants a normal life -- something that Oliver and Felicity cannot really give him. While they have done everything in their power to insulate him from the superheroics in their life, it has failed as often as it has succeeded, and his fear of abandonment was stoked in a big way when Oliver made the deal to have himself sent to prison without ever talking it over with Felicity and William.

During a fight with Oliver, he called his mother's parents and asked them to come take him away. After a brief standoff between the characters, Oliver relented and agreed that it was probably the best thing for his son.

The other departure -- that of Curtis Holt -- feels a little less significant in the world of the series. He has been largely off the board for most of the season, appearing infrequently and not featured at all in the flash-foward story.

Kellum joined the series in season four, and became an immediate and major part of Team Arrow, essentially serving as Felicity's sidekick in the same way Roy and Thea had been Oliver's. He suited up as a vigilante after a while, too, but has been in and out of the suit a handful of times over the years.

“I guess the cat’s out of the bag,” Kellum posted to Twitter. “But hey, I’m so thankful to have been a part of this amazing show for the last four years. It has truly been a pleasure to get to work with such wonderful human beings on a daily basis and to interact with all the fans who make the show possible. I will miss being int he fight week to week with my #ArrowFam, but am so excited for the direction the show is heading in. Beth and the writers are doing such an amazing job. This has been the most exhilarating experience I’ve ever had and I will definitely pop in here and there (you haven’t seen the last of Curtis Holt) in the future. Thank you David Rapaport for bringing me in to read, thank you Greg Berlanti, Marc Guggenheim, and Wendy Mericle for taking a chance on me and thank you Peter Roth and Warner Bros. and Mark Pedowitz and CW for saying yes! Thank you Stephen Amell, David Ramsey, Emily Best Rickards, Katie Cassidy, Juliana Harkavy, Paul Blackthorne, Rick Gonzalez, John Barrowman, Willa Holland, Colton Haynes, Katherine McNamara and any other actor Is got the pleasure of sharing the screen with. Most importantly, thank you to all the fans who accepted me on this fantastic journey. I’ll always get to say I was Mr. Terrific! That’s so damn cool! Excelsior!”

Arrow airs on Monday nights at 8 p.m. ET/PT, before episodes of Black Lightning on The CW.