In the popular TV series Little House on the Prairie, Alison Arngrim and Melissa Gilbert played mortal enemies on screen. However, behind the scenes, their relationship was quite different. During an exclusive interview with PEOPLE at the show’s 50th Anniversary Cast Reunion and Festival, Arngrim, who portrayed the schoolyard bully Nellie Oleson, opened up about her close bond with Gilbert, who played Laura Ingalls Wilder.

Arngrim, now 62 years old, fondly recalls how she and Gilbert, now 59, would spend time together like sisters when the cameras stopped rolling. They even choreographed their fight scenes together, starting from the first year they began working on the show in 1973. Arngrim humorously describes their friendship as “completely bonkers.”

Fans of the show often express surprise when they see a photo of Arngrim and Gilbert smiling together behind the scenes during a Christmas episode where their characters fought. People would comment, “It’s little Nellie and Laura, but you’re smiling. The two of you don’t smile at each other in that episode.” Arngrim explains, “I’m like, ‘This was us for real.’”

However, while Arngrim and Gilbert were able to separate fiction from reality, the audience wasn’t always able to do the same. Nellie Oleson had become such an iconic bully that viewers found it challenging to separate the character from the actress. Arngrim vividly recalls instances where people expressed their disdain for her character, with one person even throwing a cup of orange soda in her face during a Christmas parade.

Despite the negative reactions from fans, Arngrim has learned to embrace her role as a bully. She even did a live one-woman show called “Confessions of a Prairie Bitch,” where she shared her experiences from the show. She finds it fascinating how people become so convinced that her character is real that they react strongly towards her.

The friendship between Alison Arngrim and Melissa Gilbert on Little House on the Prairie reminds us that appearances on screen can be deceiving. Sometimes, the actors who appear as enemies are actually the best of friends off-screen.