There'll be How I Met Your Mother fans with knots in their stomach all day today as they wait anxiously for the final episode of the hit CBS sitcom. It has been a long road for the comedy show which by tonight will have run its course over nine seasons. When "HIMYM" debuted back in the fall of 2005, no one could have predicted the consistent success and comedic legacy of such a simple premise: a man in 2030 telling his two kids the tale of how he met their mother.

How I Met Your Mother Cast
'How I Met Your Mother' Prepares For Its Final Episode This Evening.

An entire series told in flashbacks, HIMYM only revealed the identity of "the mother" at the end of series eight, played by Cristin Milioti. Certain signals from her interaction with Ted (Josh Radnor) lead fans to believe that the mother actually is dead in 2030, and that's why the dad is reminiscing with his kids. This rumour was quickly played down by the cast but shows a keenness amongst fans for a "legen-dary" twist to top of their favourite show.

Equally, fans have also speculated that the guy telling stories to his children isn't Ted at all as we're lead to assume and instead another character from the catchphrase-laden comedy.

Neil Patrick Harris, who plays wise-cracking lothario Barney in the show, marvelled at the show's stamina and consistent audience (an average of 9.47 million per episode) across its nine seasons. "The first two seasons seemed very on the bubble," Harris said, via NY Daily News. "Which I thought was good for us. It gave us the opportunity to come up with our own sense of humor.

"Sometimes when a show is thrust into success right away, there are high expectations to come up with terrific stuff super fast. We got to develop a great vocabulary and weird little inside jokes. I liked the slow-burn elements," the actor added.

Watch A Clip From The Hilarious Penultimate Episode:

Show creators Carter Bays and Craig Thomas put the success of HIMYM down to the strength and versatility of its core cast, Radnor, Harris, Cobie Smulders, Jason Segel and Alyson Hannigan. "It gave us such confidence," said Thomas. "We'd just write one little line and say, 'Neil's going to do something great with that' or 'Jason [Segel, who plays Mosby's best friend Marshall] is going to do something great with that.' It's almost kind of lazy, but more trusting, like, let's let them just play."

The final episode of How I Met Your Mother and the season eight finale will air tonight at 8pm.

More: The 'How I Met Your Mother' makers recently had to apologise for racial appropriation: read more here.

More: 'HIMYM' building to a macabre finale? Find out why worried fans thought this would be the case.

Watch The 'How I Met Your Mother' Stars Arrive For Letterman: