Conan O'Brien is pretty hard to miss, due to his 6'4 frame and bright orange pompadour. So if you happened to be watching 'How I Met Your Mother' last night and thought you spotted the late-night host for a brief moment in the background of the gang's favorite bar, you certainly weren't imagining things.

Before the show aired Monday, 'HIMYM' star Neil Patrick Harris gave his Twitter followers a hint that something like this was brewing.

"Watch the new episode of HIMYM tonight and try to spot the awesomest of dudes randomly hanging out at MacLaren's. #dontblink," Harris tweeted.

In fact, if you caught Harris' appearance on 'Conan' last June, you would've known that an O'Brien cameo was coming. During their chat, the two revealed that Conan had won a walk-on role on 'HIMYM' in a charity auction they had both attended. When the show's producers heard that it was Conan who out bid everybody for the prize, they wanted to expand the role from the cameo it had been offered as.

However, Conan told them he thought it would be funnier if it remained a brief un-credited walk on. So that's the story behind Conan's very short stint on 'How I Met Your Mother.' Check it out below, courtesy of HuffPo.