The mint green festival drink, the McDonald's Shamrock Shake, that all started with charitable act by and Irish American businessman.McDonald's

The secrets behind the McDonald's best-selling Shamrock Shake have been revealed. Strangely, the bright green minty treat dates back to 1970, and its story is based around a charitable act.

The Shamrock Shake was developed in 1970, according to McDonald's. However, according to reports on Delish.com, Harold Rosen, who owned a McDonald's in Connecticut, claims he invented the popular holiday drink in 1966.

The McDonald's website says, "It all began with a little girl, a football team, and a visionary doctor."

The Philadelphia Eagles tight end Fred Hill's daughter was diagnosed with leukemia and began treatment. The Hill family were camping out in waiting rooms in hospitals and saw other families doing the same. They realized that many families who were traveling long distances to visit their sick family members had nowhere to stay and could not afford hotel rooms. The Hill family did something about it.

Hill and his team decided to raise some funds. The team's general manager, Jim Murray, called a friend in McDonald's advertising and suggested the team on the next promotional push. It just happened to be St. Patrick's Day.

Read more: Ireland’s favorite meal, St Patrick's Day bacon and cabbage recipe

Rogers Merchandising in Chicago created the shake and James Byrne, the executive artist at the firm, used a family recipe.

The Shamrock Shake raised enough money to buy a four-story house which was the first Ronald McDonald House.

Imagine, the Shamrock Shake now has 21,500 fans on Facebook and is second in popularity only to the McRib, and that sandwich had a "Simpsons" episode dedicated to it!

More importantly, the Ronald McDonald House program has also exploded in size as a much needed resource for families dealing with the difficulties of looking after a sick child in the hospital. It now has a presence in 60 countries and regions across the globe providing homes, family rooms, care mobiles, grants and scholarships that help almost 6 million families. 

Kim Hill, the girl who inspired it all, unfortunately passed away in 2011 aged 44. 

Here’s a hilarious ad for the Shamrock Shake from 1983:

*Originally published in 2013.