Killzone 2 was originally planned to launch as Killzone 3, one of the game's designers has revealed, hinting at the possibility of a cancelled PS2 follow-up to the original Killzone.

Discussing his career with Pixel Enemy, industry veteran David Goldfarb, who is now serving as game director on upcoming heist-shooter Payday 2, revealed that he "was the first designer on what was originally Killzone 3 that then became Killzone 2.

"There's a story there that I can't tell," he said, "so maybe you'll have to edit this."

Goldfarb's comments suggest that Guerrilla may have been developing a secret Killzone title meant to sandwich the five-year gap between the PS2 original and PS3 follow-up.

Killzone 2 was first revealed during the PlayStation 3's announcement at E3 2005. However, it was never officially referred to as Killzone 2, with the pre-rendered trailer simply ending with the word 'Killzone'.

It finally released in early 2009 with Killzone 3 following two years later in February 2011.

PS4 follow-up Killzone: Shadow Fall and PS Vita spin-off Killzone: Mercenary are both due to release later this year.