From left, Misha Collins as Castiel, Jared Padalecki as Sam Winchester and Jensen Ackles as Dean Winchster star in “Supernatural.” The show's 15th and final season starts at 8 p.m. Thursday on the CW Network.

LOS ANGELES — The end is finally here. The demon-fighting Winchester brothers — Sam (Jared Padalecki) and Dean (Jensen Ackles) — will be able to park their ’67 Chevy Impala as the 15th season of “Supernatural” will be the last. The journey to the conclusion begins at 8 p.m. Thursday on the CW Network.

The 15th season, which will bring the episode count number to 327, will test Sam and Dean more than any before as they find themselves dealing with God.

The longevity of the show has surprised Padalecki, who was convinced it would not last past the first episode.

“We still technically haven’t filmed the end of (the) show, so to some degree we don’t know how the show is going to end. But I’m grateful to be here after 15 years. That’s for certain.”

One reason Padalecki lacked confidence is that the actors were told in beginning by series creator Eric Kripke that he had a five-year plan for the show. Once the series reached that five-year mark, Kripke left but the production continued to gain a very loyal fan base. Continued renewals helped make “Supernatural” one of the most successful shows in TV history.

Ackles is happy “Supernatural” lived long past the original plan.

“It’s kept us all together and kept us all gainfully employed now for 15 years. And we’ve been able to continually tell this story, and it’s a story that we’re all very excited about, very passionate about. And I love these characters. I wouldn’t be sitting here if I didn’t,” Ackles says. “It’s something that means a lot to me, and it hasn’t grown old. That’s not why we’re entering into the final season. But I certainly don’t want it to grow old, which might be why, I think, we’re all wanting it to go before it does get to that point.

“This is a very special thing to me, and I want it to end in a way that does justice to what we’ve built for the past 14-and-a-half years. And I think that right now the plan that we have, the game plan that we have is going to do just that.”

As for this being the final time the Winchester brothers face monsters, it’s important to keep in mind that a running joke on the set of “Supernatural” is that nothing ever stays dead.