A man who found a fake moustache hidden underneath a water valve in his house later discovered his housemate had been planning an excruciatingly long-term dad-joke.

"Five months ago, my roommate John moved out," Reddit user Ryan Kramer explained.

"I haven't been in his room since then, however this week, behind a tiny door that accesses a water valve, we found a little surprise."

Mr Kramer says he then sent John "a confused text", to which he finally received the punchline.

"You found it! My secret 'stache!" it said.

"He has been waiting five months to make that pun," Ryan concluded.

Imgur / Ryan Kramer Credit: Imgur / Ryan Kramer

Images originally uploaded to Imgur here and posted to Reddit here.