The climate teen activist is currently in North America after sailing across the Atlantic to speak at a UN climate event in New York.
A photo of Thunberg, who follows a vegan diet - and encouraged her parents to do the same - was shared on Esther's Facebook page.
The accompanying jokey caption says: "We were gonna change the world together. But she took my last cupcake, so the future of our alliance is uncertain."
Esther the Wonder Pig
Esther became famous online after her human companions Derek Walter and Steve Jenkins acquired her believing she was a 'micro pig' - but saw her grow to a massive 600lb.
The pair say they kept Esther because it isn't her fault they were misled. "She didn't ask for the life she was given," they wrote on Facebook.
"We have the chance to provide her with the life she deserves, not the one she was bred for. What kind of people would we be to deny her that? She deserves everything we can ever give her. For Esther and for all the other pigs out there we haven’t been able to save......yet."
Walter and Jenkins went on to open the Happily Ever Esther Farm Sanctuary in Campbellville, Canada, and write the New York Times bestselling Esther the Wonder Pig: Changing the World One Heart at a Time, which documents their journey into animal activism.