Earlier this month, director James Gunn confirmed a small cameo for frequent collaborator and Firefly alum Nathan Fillion in Gunn's upcoming blockbuster, Guardians of the Galaxy. But is Fillion the only one popping up in the intergalactic Marvel flick?

Was 'Guardians of the Galaxy' Star Chris Pratt Almost in 'Avatar' and 'Star Trek?'

According to the people over at Stitch Kingdom, a cast list released by Disney reveals a few other notable names appearing during the film as well as in an after credits sequence.

The casting list includes Stan Lee as the 'Xandarian Ladies' Man,' Fillion will be 'Monstrous Inmate,' musician Rob Zombie lends his voice as the 'Ravager Navigator Voice,' and Gunn himself will appear in the film as one of the 'Maskless Sakaaran.'

New 'Guardians of the Galaxy' TV Spots Highlight Drax, Gamora Origin Stories

But Stitch Kingdom adds that one other cameo will appear, and it is another Marvel property that many thought would never make the screen again. In time for the 28th anniversary of his own film, Howard the Duck will be appearing in some capacity during Guardians of the Galaxy.

This information comes from a line in the end titles that credits co-creators Steve Gerber and Val Mayerik. Stitch Kingdom adds that they are unsure if it is just a call-back to a comic that Peter Quill (Chris Pratt) was a fan of when he was living on Earth or if Howard the Duck is making his mark within the Marvel Cinematic Universe.

Guardians of the Galaxy stars Pratt, Zoe Saldana, Dave Bautista, John C. Reilly, Glenn Close, Michael Rooker, and features the voices of Vin Diesel and Bradley Cooper. It opens in theaters on August 1.