The blink-and-you'll-miss-it appearance came after the late-night host won a role as an extra in a charity auction
Yes, that really was Conan O'Brien standing by the door in MacLaren's bar on Monday night's "How I Met Your Mother."
O'Brien revealed his cameo role on his TBS talk show last June, telling guest (and "HIMYM" star) Neil Patrick Harris that he just wanted to be an extra in the bar.
And that's exactly what he did. In the scene's final moments, a familiar tall, red-headed fella is enjoying a beer as NPH's Barney leaves.
Watch the video: