This fall, Arrow will join the rest of The CW’s DC TV shows for an epic four-part crossover. The episodes, currently being filmed in Vancouver, will bring together the casts of Arrow, The Flash, Legends of Tomorrow and Supergirl in what promises to be an huge week for the network. Series executive producer Marc Guggenheim has already teased a potential Queen family reunion for the Arrow portion of the crossover, and star Stephen Amell has been all over social media (as usual), tweeting about what fans can look forward to seeing for the 100th episode of the show that launched the Arrowverse.

In the run up, Amell has tweeted more than once about a potential guest star for the episode, and today it looks like he’s revealed the fan-favorite character who will be returning — although there are still some questions to be answered about the reappearance.

In the tweet, Amell posts a photo of himself (wearing the same outfit he is in earlier set photos) on a park bench. On the other end of the bench, sits none other than Deathstroke, in full costume, with a sword across his lap.

It’s pretty clear this means Deathstroke will be returning to the show for the 100th episode — although it’s not clear how or why just yet. Slade Wilson (Manu Bennett) appeared as Deathstroke throughout the first and second seasons of the show as a primary villain. He managed to slaughter a lot of people along the way, too, including Oliver Queen’s mother, Moira (Susanna Thompson), before eventually being caught. More recently, Wilson appeared briefly in season 3, when Oliver and Thea Queen (Willa Holland) returned to Lian Yu. Currently, Slade Wilson is presumed to still be on Lian Yu, in an ARGUS supermax prison. However, there is another option for the man in the Deathstroke suit. In Legends of Tomorrow, the Legends visited a dystopian future version of Star City where Grant Wilson (Jamie Andrew Cutler), Slade’s son, has taken up the Deathstroke mantle.

Whether it is Slade or Grant who will be appearing in the crossover event, it’s sure to delight fans. Many feel that Deathstroke is one of the best villains that Team Arrow have faced in the show, and his appearance may suggest a return to the more grounded tone of Arrow’s first two seasons. With the last season veering off into the supernatural, it would be fantastic to see the series reconnect with its roots on Lian Yu, and with a vigilante (human) archer, rather than magic-wielding foes. Deathstroke’s reappearance could also be connected to ARGUS, connecting the villain to the government agency and tying up the final year’s worth of “island” flashbacks neatly this season.

Of course, there are other possible ways that Deathstroke could be returning that wouldn’t have the same impact on the show. Flashback are a big part of the Arrow world, for better or for worse, and it’s possible this is how Deathstroke returns. Time travel is now also in play thanks to Legends, and let’s not forget the effects of Flashpoint. Until Amell tweets a new image of Deathstroke without his mask, we’re just going to have to wait until the 100th episode to find out exactly what is going on.

The Flash season 3 will premiere Tuesday October 4 at 8pm on The CW, Arrow season 5 will premiere in the same timeslot on Wednesday October 5, Supergirl season 2 on Monday October 10, and Legends of Tomorrow season 2 on Thursday October 13.