Why is McDonald’s selling Shamrock Shakes in Philly right now?

Philadelphians watching the Eagles’ season opener on TV had a reason other than Carson Wentz to rejoice on Sunday: A McDonald’s commercial announced that Shamrock Shakes — the chain’s mint-flavored St. Patrick’s Day milkshake — would be available in Philly for a limited time.

“It’s a Philly original that’s ready to rock the tastebuds of Eagles fans across Philly,” the announcer narrated. “Fly to get yours today.”

Footballs fans and milkshake fans celebrated together.

The shake will be sold at McDonald’s in the city through Oct. 18. And while the overwhelming sentiment on social media was jubilant or envious, some did express bewilderment.

The most obvious connection between the jade-colored treat and the Eagles being the color green, some wondered why Jets or Packers fans weren’t getting a St. Patrick’s Day gift in September.

In fact, the Eagles and the Shamrock Shake — while not actually minted in Philly — go way back, to 1974.

It was then that Eagles general manager Jimmy Murray collaborated with Dr. Audrey Evans, an oncologist at the Children’s Hospital of Pennsylvania, on providing young cancer patients and their families a place to stay while undergoing treatment.

The Eagles had been fundraising to help pediatric cancer patients since 1972, when tight end Fred Hill — whose daughter, Kim, had been diagnosed with leukemia — and a neighbor started the charity Eagles Fly for Leukemia. With support from then-Eagles owner Leonard Tose and Eagles players, they had managed to raise enough to help complete the oncology wing at CHOP’s new home on Penn’s campus (it moved from Center City).

But in 1974, Murray and Evans turned their attention to getting a house for cancer patients’ families, a project that would require more money.

So Murray, a Philly native, called up a friend at an ad agency representing the area’s McDonald’s to see what they could work out. It happened to be around the time that the Shamrock Shake — then a four-year-old promotion without much of a following — was about to hit the market. Murray asked if local owners would be willing to donate 25 cents of every shake sold to the house effort.

But when the ad agency ran it past McDonald’s execs, they had a question: If they donated all the proceeds from Shamrock Shakes, could they name it the Ronald McDonald House?

Murray replied that, for that money, they could name it the Hamburglar House.

The first Ronald McDonald House was a seven-bedroom house at 4035 Spruce St. in West Philly. When it opened on Oct. 15, 1974, McDonald’s founder Ray Kroc, Mayor Frank Rizzo, Tose, and the Eagles were in attendance, as was Fred Hill and his daughter (who lived to the age of 44).

The charitable promotion spread to other cities, starting with Chicago, then to Denver and Boston, Atlanta and Los Angeles, with area football teams partnering with McDonald’s on the promotions. Ronald McDonald Houses proliferated around the U.S. and eventually the world, and the Shamrock Shake became a seasonal staple with a devoted audience. (It was discontinued in the 1990s, but brought back in the ’00s due to customer demand.)

Today, sales of the shake don’t necessarily go to Ronald McDonald House — local franchises can choose to donate proceeds — but the chain still donates to the organization. A significant amount of funds are also raised via donation boxes in restaurants.

So if you enjoy an out-of-season Shamrock Shake, think about dropping the change in the Ronald McDonald collection box, and thank the 1970s-era Eagles. Go Birds.