Cristin Milioti
Reuters Cristin Milioti

As How I Met Your Mother enters its final episodes, one fan theory regarding how it might end has been gathering a lot of steam.

Episode 19, Vesuvius, seemed to reinforce the fan speculation, but now the show's star and the titular mother Cristin Milioti has rubbished the theory – calling it "crazy".

Warning: If you don't want to read the fan theory, do not read on.

For some time now fans of the nine year old sitcom have theorised that the mother might well have been dead the entire time Bob Sagat has been narrating the show as Ted Mosby.

"That's insane," Milioti tells The Hollywood Reporter the day before the show's final day of filming. "There are some crazy conspiracy theories, which really makes me love the fans more... That is so crazy."

Calling the final episode – which airs in the US on 31 March – "beautiful", the actress also says that they did not film multiple endings in an attempt to maintain secrecy.

"They've had this vision for nine years, and it's in great hands," she says of co-creators Carter Bays and Craig Thomas. "They know exactly what they want to do."

In a flash forward scene involving Ted (Josh Radnor) and the as-of-yet unnamed mother, she describes her husband as someone "who lives in his stories" and that he shouldn't because "life only moves forward".