Though fans will still need to wait until Monday to find out just how How I Met Your Mother ends its nine-season run, one of the show's stars has revealed that he knew how it would end from the very beginning.

Mother Death Theory Resurfaces?

Josh Radnor, who has played Ted on the hit series for all nine seasons, revealed to The Hollywood Reporter March 24 that he's known a big part of the finale since the show's first season.

"I was let in on a big thing [in the] first season," Radnor said. "I thought they weren't going to do that, and then they said, 'No, we're still doing that.'"

'Fun, 'Random,' Guest Star Appearing in Finale?

Though Radnor won't reveal what it was he knew, it could have something to do with his character's kids, Penny and Luke (Lyndsey Fonseca and David Henrie). Series co-creators Carter Bays and Craig Thomas previously revealed in January that the final scene of the series was filmed eight years ago, and includes the two kids.

At the time, Bays and Thomas revealed that they had decided to include the kids in the final scene years ago, but had to film it in advance because the kids are not supposed to age on the show. As a result, the scene was filmed back during the second season, and the two young actors signed non-disclosure agreements that swore them to secrecy.

While most aspects of the finale still remain secretive, Thomas revealed to TV Guide on March 18 some teasers about some things fans can expect in the final hour of the series.

The hints he gave included a robot wearing a tuxedo, the fateful scene at the Farhampton Train Staton where Ted and the Mother will finally meet, and finally, her name.

The How I Met Your Mother series finale airs Monday, March 31, at 8 p.m.