Billy Joel's daughter Alexa Ray Joel reacted to his normal pressure hydrocephalus (NPH) diagnosis in an Instagram post shared on May 24, a day after the musician revealed he is dealing with the condition.

Ever since I first played “The Firefly Lab,” the final mission in The Last of Us, which was later revisited in the show’s Season 1 finale, I’ve been able to understand and justify Joel’s decision to save Ellie from the Fireflies and prevent them from using her to make a cure (one that may or may not have worked).

Potts: NPH is a form of hydrocephalus, a build-up of CSF in the brain. It's typically seen in older patients, usually over the age of 60. It's called "normal pressure" because, unlike most other types of hydrocephalus, the pressure doesn't go high, but it still has an effect on the brain.

Christie Brinkley and Billy Joel have been the friendly exes and that is on display after his recently shared medical diagnosis.