McDonald's Wiki

The Shamrock Sundae was introduced in 1980, which consisted of vanilla ice cream topped with a mint green Shamrock syrup.

For over 50 years, the Shamrock Shake as delighted McDonald’s fans. Originally created by Hal Rosen, the instantly successful frozen food treat has people counting the day till the limited time offering re-appears.

it did not choose to bring back the Shamrock Sundae. In 1980, there was a limited time offering of vanilla soft serve topped with mint green Shamrock syrup. For those who enjoyed that vintage treat, the minty color and flavor seemed to put a little spring in their step.

McDonald's first sold the Shamrock Shake in 1970. Over the years, the burger chain has brought back the original as well as variations like the "Shamrock Sundae" in 1980, a chocolate version in 2017 and the Oreo Shamrock McFlurry in 2020. The Shamrock Shake, originally sold regionally, went on sale nationally in 2012.