Be warned, there will be a minor spoiler for Guardians of the Galaxy below, so if you don't want to know who Nathan Fillion is reportedly playing in Marvel's Phase Two adventure, stop reading right now.

Last week, a report surfaced that Nathan Fillion has a cameo appearance as Nova (a.k.a. Richard Rider) in Guardians of the Galaxy, which turned out to be both true and false. Director James Gunn confirmed on Saturday that Nathan Fillion is not playing Nova, but the actor does have "a very small fun cameo he did as a favor..."

While fans have been trying to figure out who Nathan Fillion might be playing, Schmoes Know's source has the scoop, revealing that the actor is actually only lending his voice for the cameo role.

"Nathan Fillion will be voicing the part of Cosmo, the psychic Russian cosmonaut dog that has appeared in the Guardians of the Galaxy comics."

It has already been confirmed that the Knowhere space station will be featured in Guardians of the Galaxy. In the Marvel comic books, Cosmo was the security chief of Knowhere who later becomes a member of the Guardians.

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It isn't known if Nathan Fillion will only be lending his voice, or if he will portray Cosmo through the motion-capture technology they used for Rocket Raccoon (Bradley Cooper) and Groot (Vin Diesel).

Naturally, this report has not been confirmed by Marvel Studios, but are you more excited for Guardians of the Galaxy if Nathan Fillion is voicing Cosmo? Chime in with your thoughts below. Nathan Fillion previously starred in director James Gunn's first two features, Slither and Super.