'How I Met Your Mother' Final Season Teaser: Who Will Ruin Barney and Robin's Wedding? (Video)

A 30-second preview also promises more about Ted's wife (finally!) and "the final slap."

The beginning of the end of CBS' How I Met Your Mother is less than a month away.

In a teaser for the final season premiere, set to air Sept. 23, Robin (Cobie Smulders) and Barney (Neil Patrick Harris) are forced to confront the question of who will ruin their big day.

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"Someone is going to ruin this wedding," Robin says in the clip.

"It's just a question of who," Barney adds.

Will it be Marshall (Jason Segel), who's shown on an airplane yelling that he intends to wreck the ceremony? Will it be Ted (Josh Radnor), whose lingering feelings for Robin are alluded to in flashbacks from last season and who is shown getting tackled by Lily (Alyson Hannigan) as he gives Robin her locket?

We'll have to tune in to see, but the promo did promise that the final season -- in addition to, at last, showing us more of the titular mother -- will include the "final slap," a reference to the ongoing slap bet Marshall and Barney made in season two.

Watch the full preview below.