While Michael Landon had nine children of his own, he was a father figure to many others, including his Little House on the Prairie costar Melissa Gilbert. So, it was just as hard for her when Landon was diagnosed with pancreatic cancer and died three months after announcing his diagnosis to the world.

Little House on the Prairie star Melissa Gilbert is opening up about the devastating illness that plagued her co-star Michael Landon. The actress, now 60, played the iconic Laura Ingalls Wilder on the popular series throughout the 1970s and 80s.

Melissa Gilbert opens up to PEOPLE about witnessing how “brutal” Michael Landon’s and Patrick Swayze’s battles with pancreatic cancer were and how that inspired her new partnership with PanCAN, a charity for the disease.

Michael Landon, who starred in "Bonanza" and "Little House on the Prairie," died in 1991 at age 54. The cause of death was pancreatic cancer. He died three months after announcing his diagnosis.