Warning: The following contains SPOILERS for Harley Quinn season 3, episode 5, "It's A Swamp Thing."In Harley Quinn season 3, the heroes engage John Constantine in a drinking contest that ends with a reference to the Laughing Magician's onetime romance with King Shark. The nod was doubly amusing, given King Shark is a regular member of the ensemble of Harley Quinn's HBO Max animated series. Sadly, for those fans who ship the strange couple, the relationship was not actually depicted on or off camera.

The story of Harley Quinn season 3, episode 5, "It's A Swamp Thing," found Harley Quinn and Poison Ivy in New Orleans, trying to track down Swamp Thing. The warlock John Constantine, who has a history of Swamp Thing team-ups, offered his assistance in finding the elusive elemental, but only if the two women could best him in a drinking contest. Since the alternative was having an honest conversation with an already drunk Nora Fries (who had tagged along on the trip) Ivy accepted the challenge.

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Morning found the three anti-heroes passed out on the barroom floor. It was evident the preceding night was quite wild, and the unconscious Constantine was shown to be wearing a t-shirt which read "I TANKED THE SHARK," with a stylized shark fin in place of the "A" in shark. This was a subtle nod to the animated movie Justice League Dark: Apokolips War and a subplot that revealed that John Constantine had once been romantically involved with King Shark.

The Constantshark Ship Explained

Harley Quinn Show John Constantine Poison Ivy Drunk On Bar Floor

One scene in Justice League Dark: Apokolips War showed John Constantine working with Raven and Robin to find information in an underground fight club run by the Suicide Squad. John seemingly flinched upon seeing several Squad members, saying he'd just seen his ex. Raven presumed he was referring to Harley Quinn, but it turned out John was referring to King Shark.

Since that time, the "Constantshark" ship has been referenced by numerous fan artists online and depicted in several works of fan fiction. Actor Matt Ryan, who played John Constantine in the Arrowverse and in Justice League Dark: Apokolips War, confirmed that he was aware of the ship in a virtual Wizard World convention panel and said he hoped Constantine might one day encounter the Arrowverse version of King Shark. Sadly, circumstances forced Ryan to retire from the role on Legends of Tomorrow before this could come to pass, but it is nice that Harley Quinn season 3 allowed him a chance to play John Constantine once more and made reference to Constantine's most infamous romantic relationship, even if it didn't allow him to hook up with the Harley Quinn version of King Shark.

Harley Quinn season 3 airs Thursdays on HBO Max.