In casting news that can only be described as "legendary," Neil Patrick Harris is close to signing on for a guest-starring gig on Glee.

Reliable sources, such as Entertainment Weekly and E! News, confirm the star will likely appear in an upcoming episode directed by Joss Whedon, which will reunite the pair responsible for Dr. Horrible's Sing-Along Blog.

"The plan is for Neil's acting, singing and dancing talents to all be used," said a Glee insider.

Neil Patrick Harris on Glee? We're as shocked as Barney is!

Because Harris stars on How I Met Your Mother, CBS, must sign off on the contract. But both shows are produced by the same studio (20th Century Fox) and air in different timeslots.

In other words: this might as well be a done deal. Let the screaming commence!

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.