An impending personal tragedy has caused Fiona Apple to cancel her upcoming tour of South America. In a long, handwritten letter posted to her Facebook page today (Nov. 20), she reveals the reason: the terminal illness of her dog, Janet.

"She has Addison's Disease," Apple wrote. "Which makes it dangerous for her to travel since she needs regular injections of Cortisol, because she reacts to stress and to excitement without the physiological tools which keep most of us from literally panicking to death."

Apple found Janet, a pitbull, 14 years ago in Echo Park when Janet was four months old. The singer says that the dog has been the "most consistent relationship of her adult life" and they have been together, with the dog remaining "effortlessly joyful and playful" through all their ups and downs.

However, Apple noticed a change in Janet when upon returning home from her U.S. tour and realized the end is near. So rather than run the risk of Janet dying while she is on tour, Apple has decided to stay home and be with beloved dog in her final days.

Apple did not say when, or if, the South American tour will be rescheduled.