The precious memory quickly racked up over 58,000 likes and hundreds of comments from royal well wishers, who were quick to spot a big difference between the royal sisters.
In the photograph little Eugenie sports a New York Mets cap while older sister Beatrice wears a Red Sox team hat, causing a divide amongst royal sporting enthusiasts.
"Beatrice representing the Boston Red Sox! Love it!!" one user wrote.
"OMG let's go Mets!" a rival supporter said.
Eugenie and Beatrice enjoy a famously close bond.
WATCH this video to see the younger Princess of York describe her beloved sister Bea!
The Queen's granddaughters are also wearing Canadian Roots jackets in the photo which got plenty of praise from followers, Hello! magazine reports.
One fan was more preoccupied with Eugenie's current situation though, sending her love and asking if a royal baby announcement could be on the cards for her and husband Jack Brooksbank.
"Can't wait until we get a Royal Baby Brooksbank - you're my favourite royal couple!"