How I Met Your Mother is expanding the lineup of guest stars for its final season.

Show co-creator Craig Thomas took to twitter recently to tease another as-of-yet unnamed guest star.

"Just booked an amazing musical guest for our "Slapsgiving 3" episode...stay tuned!" he tweeted on October 11.

The tweet has had many wondering who the musical guest could possibly be, with Carter Matt speculating that it could be Blurred Lines singer Robin Thicke.

On the website, Carter Matt explains why Thicke would be a perfect guest star for the episode, saying, "For one, he's the sort of guy who Lily would go crazy over, just as she crushes over many a man with show-business ties. Also he's the son of former How I Met Your Mother guest star Alan Thicke, and maybe this gene for performing on the show really runs in the family."

There is no confirmation on whether Thicke would actually be the guest performer, and an official synopsis for the episode, set to air on January 13, has not been released.

One guarantee for the episode if that it would mean Marshall (Jason Segel) has finally gotten to Farhampton and will be on time for Robin (Cobie Smulders) and Barney's (Neil Patrick Harris) wedding, after he has been struggling to get there all season. According to The International Business Times, A 'Slapsgiving' episode cannot happen without Marshall physically present, due to the history behind 'Slapsgiving.'

An episode which aired during season 2 titled Slap Bet saw Marshall and Barney betting the right to slap the loser as many times as he wanted with no warning or expiration date, after they tried to determine whether or not Robin had done porn when she was younger. Barney ended up losing the bet, and so far, Marshall has only used six of his eight slaps-twice in season 2, once in season 3, once in season 5, and twice in season 7.

How I Met Your Mother airs Mondays at 8 p.m. on CBS.

Tags: How I Met Your Mother How I Met Your Mother Season 9 Spoilers CBS television