It's long been believed to be nothing more than an urban myth, but now a McDonald's manager has confirmed the existence of the fast-food chain's "secret menu."

In a thread on Reddit, the staff member from Glasgow, who goes by the username orchidhibiscus, revealed that off-the-menu orders can be taken, including one burger known as the McGangbang.

Under the thread name "I Am A McDonald's Manager Ask Me Anything," the worker said customers can "add, remove or change ingredients by special request. These are called 'grill orders' (i.e. Big Mac no pickle)," according to People.

However, being able to order items off the official menu is simply a matter of who is behind the counter, said the manager.

"Order one and the workers might not know it by name," the manager wrote, according to Us Weekly. "But if you explain what it is, and are willing to pay for all the ingredients, it's just another 'grill order' that we can make up."

Two notable items on the "secret menu" are the McGangbang, a McChicken sandwich enclosed within a McDouble and the Monster Mac, a Big Mac that includes eight (or more) beef patties.

The manager also gave a brief guide on what to definitely avoid, reported the Daily Mail. "DON'T order... the grilled chicken. It's horrible frozen chicken that we defrost and steam and it's a bit gelatinous."

The "secret menu" was first bought to the public's attention last April when culinary insiders Hack The Menu revealed several ways customers could enhance their Happy Meal with off-the-menu products.

In response to the manager's claims on Reddit, a spokesperson for McDonald's said: "There is no secret menu at McDonald's UK."

In fact, the "secret menu" has become so widely discussed that it is now listed as an FAQ on the company's website. They did, however, acknowledge that customers can ask for changes.

"Any requests for extra items or changes to our products are considered at the restaurant manager's discretion and any additional items may be charged for."