The following contains that spoiler from the Season 16 finale of CBS’ NCIS.

Rule No. 6 tells us, “The best way to keep a secret? Keep it to yourself.” And that is pretty much what CBS’ NCIS did, to pull off its season-ending jaw-dropper.

“Hello, Gibbs. No time for pleasantries — you’re in danger,” Ziva said upon bounding down the stairs to Boss basement workshop. “Well, aren’t you gonna say something?”

“Ziva” is all Gibbs could say, his mouth letting slip a faint smile.

TVLine has learned that to keep Cote de Pablo’s return as Ziva David under wraps, the finale’s final scene was never included in any script or call sheet; only showrunners Frank Cardea and Steven D. Binder held copies of the scene pages; the scene filmed with a skeleton crew at midnight, after the full crew had been wrapped for over an hour; and de Pablo arrived to the stages via a back gate entrance, to film the scene with series lead Mark Harmon.

As for what it all means moving forward…. “This surprise moment is just the beginning,” Cardea and Binder shared in a statement. “We are thrilled to share that Cote de Pablo will guest star in the NCIS Season 17 premiere this fall, as Ziva’s warning to Gibbs unfolds.”