CENTURY CITY, Calif. -- Guess who has known the ending of CBS's "How I Met Your Mother" since 2006? The actors playing the poor kids who have to listen to their long-winded narrator dad (voice of Bob Saget) tell the story of how he met their mother over nine seasons and more than 200 episodes.
Actors Lyndsy Fonseca, who went on to star in The CW's "Nikita," and David Henrie, best known for Disney Channel's "Wizards of Waverly Place," filmed their reaction shots to the conclusion of their father's story in the show's second season. The film was locked in a vault, and the actors have kept the secret ever since.
"The beginning of season two, we shot part of what is going to air in the series finale with those kids who are now 53 and 62," joked series co-creator Craig Thomas during a January set visit. "We shot that little bit with the kids in fall of 2006, and it's part of the end game. You will see it on March 31, and it's really weird to get to that point."
"How I Met Your Mother" wraps up its story Monday with a one-hour episode (8 p.m., KDKA-TV), "Last Forever," that concludes the story, although a spinoff, "How I Met Your Dad," featuring a whole new set of characters, is in development for a potential slot on CBS's fall lineup.
When it debuted in September 2005, "HIMYM" was a daring gamble for more traditional CBS. It was serialized with a mystery element (who's the mom?). It was shot like a three-camera sitcom but without an audience (audiences watched episodes after they were complete and their laughs were recorded to create the show's laugh track).
"HIMYM" follows a group of New York friends: Ted (Josh Radnor) initially dated Robin (Cobie Smulders) before a series of other women. Eventually Robin got romantically involved with horndog Barney (Neil Patrick Harris). Married couple Marshall (Jason Segal) and Lily (Alyson Hannigan) had their ups and downs but usually remained more grounded. The show uses a framing device whereby an older unseen Ted tells his kids, perched on a sofa in 2030, the story of how he met their mother.
"HIMYM" wasn't always a hit. Ratings were poor in its first few seasons before it blossomed into a popular Monday night comedy. Had the show been canceled in its first year, series co-creator Carter Bays said one of Ted's early girlfriends, Victoria (Ashley Williams), probably would have been revealed to be the Mother.
"The first two seasons seemed very on-the-bubble the entire time, which actually I thought was good for us and for the show," Mr. Harris said. "It gave us the opportunity to come up with our own sense of humor. Sometimes when a show is thrust into success right away, then there's high expectations for them to come up with terrific stuff super fast, and we got to develop a great vocabulary and weird little inside jokes so that by the time fans started watching it Netflix-style and syndication-style, it had found its own voice. I liked the slow-burn elements to our show."
At the end of season eight, "HIMYM" introduced the still-nameless Mother (Cristin Milioti) and the current season nine, set entirely over the weekend of Barney and Robin's wedding, has been an experimental stretch the showrunners never expected.
"We really did have an eight-year plan from the pilot," Mr. Thomas said. "We kind of knew how we wanted to end it, which turns out to be [at the end of] nine years."
"We'll cop to, like, it was different, the decision to do the whole [season] over a weekend. There's been pitfalls in it," he acknowledged. "But you give yourself challenges. That's why you get up in the morning, and it's been a fun challenge to figure out how to do that and also a huge part of that is meeting the mother and being able to write that."
The series finale, written by Mr. Thomas and Mr. Bays and directed by series director Pamela Fryman, will wrap up the entire story. Nothing is being left on the table for the possible spinoff series, although the creators don't rule out revisiting some of the "HIMYM" characters a few years down the road if "How I Met Your Dad" is a success.
"We owe it to this show to end it on its own terms, and when this show ends, that's the curtain coming down for this world," Mr. Bays said, noting that the finale will tell viewers why Ted chose to start the story when he did.
As for how it ends, that remains a mystery, although some principal cast members knew it before the table read for the last episode.
"I cornered Carter and Craig at our Christmas party, and after, like, five drinks, I got them in the corner, and said, 'Now it's time. I want you to tell me everything. Spill the beans. Tell me how it all ends,' and they did," Mr. Harris said. "It's more complicated than you would assume. And for all of our fans, they will be far from disappointed."
Right now, fans seem nervous, gnashing their teeth over theories that the show ends with the revelation that the Mother is dead.
"We're excited about this ending, and it's an ending that we've been really excited to tell for a long time," Mr. Bays said. "Not to oversell it because you might hate it. You might see it and hate it, but I think we forget that there is this mystery and that there is this sort of feeling that there's something unanswered because we're also telling these stories about all five of these characters and the rest of their lives."
As for the actors playing Ted's kids who have known the ending since 2006, Mr. Bays said when those actors returned to film a spoof segment that debuted at last summer's Comic-Con, "We reminded them, 'You guys have been walking around with the secret,' and Lyndsy didn't even remember it."
TV writer Rob Owen: email@example.com or 412-263-2582. Read the Tuned In Journal blog at post-gazette.com/tv. Follow RobOwenTV on Twitter or Facebook.