Marvel's Agents of S.H.I.E.L.D. season 6's most shocking moment just happened: Melinda May (Ming Na Wen) murdered Sarge (Clark Gregg), the doppelganger of the late Phil Coulson, in cold blood! The unthinkable event occurred at the very end of "Collision Course Part II" after S.H.I.E.L.D. stopped Sarge's plan to detonate an atom bomb to kill Izel (Karolina Wydra), Agents of S.H.I.E.L.D. season 6's real villain and the creator of the alien planet-killers called the Shrike.

In "Collision Course Part 1", S.H.I.E.L.D. Director Mack Mackenzie (Henry Simmons) reluctantly recruited Sarge's help in dealing with Izel and the Shrike. Perhaps the deadliest threat the Agents of S.H.I.E.L.D. have faced, the Shrike infects the inhabitants of the planets they seek to destroy (turning them into grotesque entities that resemble the crystalline structures of Superman's Krypton). Sarge and his team have been fighting Izel and the Shrike across many worlds. However, despite his resemblance to Coulson, Sarge has behaved the opposite of the beloved former Director in every way. Sarge betrayed Snowflake (Brooke Williams), his own teammate, and left her behind to die in an atomic explosion. Sarge then commandeered Zephyr-One but lost a brutal fight to Mack and was locked up in the brig. Thankfully, Jaco (Winston James Francis) finished Sarge's mission and sacrificed himself to destroy Izel's spaceship.

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Sarge remained locked up at the Lighthouse as S.H.I.E.L.D. celebrated a well-earned victory party for saving the world yet again and the return home of Leo Fitz (Iain De Caestacker) and Jemma Simmons (Elizabeth Henstridge) from outer space. But after the party was over, May entered Sarge's cell and shot him three times in the chest before delivering a headshot! "Collision Course Part II" ended with Sarge seemingly dead by May's hand.

May harbored the most animosity towards Sarge of all of the Agents of S.H.I.E.L.D. because she was in love with Phil Coulson; they spent his final days together in Tahiti and she watched him die. Although the other Agents like Daisy Johnson (Chloe Bennet) were unnerved by Sarge being Coulson's genetic double, May especially despised Sarge ever since he appeared in the Agents of S.H.I.E.L.D. season 6 premiere and immediately murdered one of their Agents. May was even kidnapped by Sarge, who taunted her about the affection she has for "this Coulson guy", but Melinda managed to capture him.

At the victory party, May even confessed to Yo-Yo Rodriguez (Natalia Cordova-Buckley), "I should have killed him the moment I saw him." After everything they've been through with Sarge, it's quite clear he's nothing like Phil Coulson despite their mysterious DNA match. Still, no matter how much she hates Sarge, it's totally unlike May to just murder him without remorse, so there's much more to this act of vengeance than meets the eye.

Now, it's possible that Sarge either isn't really dead or could still manage to come back. When Sarge and Izel had a verbal confrontation in "Collision Course Part II", the mystery woman indicated she knows who Sarge actually is and that she knows his real name, which he himself has forgotten. Furthermore, Izel's barb to Sarge - "Whose skin are you saving now? Just the one you're wearing, I hope" - allude to a new wrinkle to the mystery of how Sarge resembles Coulson. Is Sarge some kind of shapeshifter or was Coulson somehow cloned but with a mind in a tabula rasa state that was infused with Sarge's personality?

The answers to the major questions surrounding Sarge are sure to be revealed in season 6's final episodes, but fans can look forward to some major teases at San Diego Comic-Con next week when Marvel's Agents of S.H.I.E.L.D. take over Hall H for the first time.

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Marvel's Agents of S.H.I.E.L.D. airs Fridays @ 8pm on ABC.