Cobie Smulders and Clark Gregg

Fans lucky enough to attend the Marvel's Agents of S.H.I.E.L.D. panel at Comic-Con last week were privy to one of the best-kept secrets in the Whedonverse: Minutes into the screening of the series premiere, Cobie Smulders made a surprise cameo, reprising her Avengers role as Agent Maria Hill.

Scoop: Cobie Smulders makes her way to Marvel's Agents of S.H.I.E.L.D.

In the premiere, Hill helps Agent Coulson (Clark Gregg) assemble a select group of agents from the worldwide law-enforcement organization known as S.H.I.E.L.D., which investigates strange and unknown occurrences around the globe. Though many suspected — or desperately hoped — that Smulders would make her way to S.H.I.E.L.D., her role in the highly anticipated drama was surprisingly kept under wraps. Thank, or curse, Maria Hill for that.

"Like Maria Hill's a very highly trained S.H.I.E.L.D. official, I'm a very highly trained not teller of news to anybody," Smulders jokes. "Literally, even when I'm talking to friends, I'm like, 'Can I just tell you that I came from the S.H.I.E.L.D. set? Can I even say that? No.' Obviously when I did it, it was told to me not to say anything. As I was doing press for Safe Haven, a movie that I did a while ago, people kept asking about S.H.I.E.L.D. — at that point I had signed on, but I hadn't done it — so I was like, 'You know, it's a great project. If Maria Hill can be part of the universe, great. Clark's involved and he's the best.' It's nice that it's something I can finally talk about."

Smulders says Whedon initially contacted her via email to appear on the show, which also features the return of Gregg, whose character died at the end of The Avengers. "He thought that it would be cool if Maria Hill — and it's so true — was able to basically tell the audience that Coulson is alive," she says. "It's the best job ever."

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But it's still unclear if Coulson really lives, as fans hope. Spoiler Alert! In the pilot, we quickly learn that Coulson believes that he died briefly, but was then revived. In another scene, Hill notes that Coulson can never know the truth about his death, possibly giving credence to our theory that Coulson is a Life Model Decoy. "That's what everybody thinks," Smulders says. "I thought about that as an option for sure. But that was also the cool thing about it — that she's in on that serious secret. What does that mean? I don't even know, but it was so cool."

Smulders is staying mum as to whether she'll be back for more. The 31-year-old actress is only slated to appear in the premiere, but with How I Met Your Mother coming to an end, fans can only hope she'll return next season. "We don't have anything scheduled or figured out yet," Smulders says. "It's a great show. [Executive producers] Jed Whedon and Maurissa Tancharoen, who are running it, are fantastic, and obviously Joss Whedon, if he's around, he's going to be a little bit busy come the New Year. I loved everybody, but they're an amazing group of actors, so I feel like we'll see if there's even time for Maria Hill to come back because they're just going to have such great story lines anyway."

Do you hope Smulders returns to S.H.I.E.L.D. for more? Hit the comments!

Marvel's Agents of S.H.I.E.L.D. premieres Tuesday, Sept. 24 at 8/7c on ABC.