The family of Reese’s Peanut Butter Cups inventor H.B. Reese is tearing its current recipe to pieces.

Brad Reese—the grandson of the man who created the beloved candy—accused The Hersey Company of being disingenuous and “quietly replacing” the cups’ signature milk chocolate exterior and peanut butter center with different ingredients.

“My grandfather, H. B. Reese (who invented Reese’s), built Reese’s on a simple, enduring architecture: milk chocolate + peanut butter,” he wrote to Hershey corporate manager Todd Scott in an open letter posted to LinkedIn Feb. 14. “Not a flavor idea. Not a marketing construct. A real, tangible product identity that consumers have trusted for a century.”

Brad alleged that Hershey—which bought the rights to produce Reese’s Peanut Butter Cups in 1963—have replaced “milk chocolate with compound coatings and peanut butter with peanut-butter-style crèmes across multiple Reese’s products” in recent years.

“Right now, the Reese’s story is diverging from what’s inside Reese’s products,” he continued. “And that divergence puts Reese’s and the legacy behind it, at risk.”