In the recent sixth season finale, Castiel was transformed into a god and turned against his old allies, the Winchesters.
"When it comes to Supernatural, our philosophy is that everyone moves in and out and weaves in and out of the story, obviously with the exception of Sam (Jared Padalecki) and Dean (Jensen Ackles)," Gamble told TV Line.
Castiel, originally a benevolent angel, was introduced in the CW drama's fourth season premiere, with Collins being promoted to series regular for the fifth and sixth seasons.
"We love Misha [and] we love and adore the character of Castiel," continued Gamble. "His character developed to this extent and went in this unexpected direction because we were so inspired by him."
She described Castiel's transformation as "a very pivotal moment in [the character's] development".
"Basically, that's what we'll be exploring next season, so there's just a big change," she said.
The producer also confirmed that Collins will reappear in the seventh season premiere, but refused to confirm how large a role the actor will have on the show beyond that point.
"[I can't discuss it] without giving away a lot about the premiere," she explained.
Supernatural will return to Fridays at 9/8c in the fall on The CW.
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