Peacemaker wrapped its second (and possibly final…?) season last night, and featured the DC Universe debut of Checkmate, a spy-and-superhero organization seen in the comics. Checkmate’s co-creator, Paul Kupperberg, is apparently a Peacemaker fan, because he responded on Facebook in more-or-less real time, sharing a screenshot from the show with the caption “Wait! WHAT–?!”

In the episode, Checkmate is introduced as a group established by the 11th Street Kids, Peacemaker’s team of A.R.G.U.S. ex-pats and also-ran superheroes. The revelation came near the end of the episode, and while a number of friends and fans commented that they had seen it coming, Kupperberg didn’t.

“I thought it was going to be the Pax Institute,” Kupperberg said on Facebook, admitting that he hadn’t read Greg Rucka‘s fan-favorite Checkmate series, which featured the character of Sasha Bordeaux. Bordeaux, who also played a key role in Peacemaker‘s second season, was a key clue for those who expected Checkmate to come up.

In the comics, Checkmate first appeared in Action Comics #598, in a story by Kupperberg and the late artist Steve Erwin. It served as a successor/companion to “The Agency,” which had appeared in Vigilante comics (another connection to the Peacemaker show).

The original Checkmate comic series (stylized Checkmate!), featured crossovers with other “secret government organizations” in the DC Comics universe, most notably in the Suicide Squad crossover “The Janus Directive.” The group is led by leadership named after chess pieces, including black and white kings and queens, with some of those figures generally being anonymous and others being known to readers and everyday agents.

The organization took a turn for the more morally gray in the comics in the mid-2000s, when DC revealed that Checkmate’s Black King was longtime Justice League ally Maxwell Lord, who had weaponized the organization against metahumans using the OMAC satellite. After being discovered, Lord murdered Blue Beetle (Ted Kord), and became an outright supervillain — although Checkmate itself eventually rid itself of his influence and became the “good guys” again in the aforementioned second volume of comics, written by Greg Rucka and featuring Bordeaux in a key role.

In the (film and TV) DC Universe, Maxwell Lord is played by Sean Gunn, the brother of DC Studios chief James Gunn, who has suggested Lord’s character will be more like his original comics depiction in Justice League International: greedy but well-intentioned, rather than hateful and homicidal.

Gunn has also suggested Peacemaker may not return for a third season, although he does have plans for the characters and concepts introduced in the show.

Checkmate previously appeared in Smallville, with existing DC Universe characters Amanda Waller and Maxwell Lord involved. It also plays a role in the animated series My Adventures With Superman.

Peacemaker, which stars John Cena, Jennifer Holland, Danielle Brooks, Freddie Stroma, and more, airs on HBO Max. The first season is available on Blu-ray. Episodes of the second season are not yet available to purchase on digital platforms.