Billy Joel's ex reacts to his brain disorder diagnosis

Christie Brinkley just reacted to Billy Joel’s brain disorder diagnosis of normal pressure hydrocephalus (NPH).

Taking to her official Instagram account she penned a note to her ex-husband, starting it off as a letter to him.

"Dear Billy," she wrote, adding, "The whole Brinkley gang is sending you lots of love and good wishes for a full and speedy recovery."

Uploading a clip from one of the Piano Man hitmaker’s concerts as well as a video of him and their daughter, Alexa, backstage, she further mentioned, "I was looking for some cute photos of you and Alexa to send you, when I came across this clip from a recent concert.”

"It reminded me of all the joy you create, and all the sensational sing-alongs you've led. You turn an arena of strangers into a living room full of friends as we all sway in unison,” the American model added.

Christie continued, "I'm sure I'm speaking for everyone in that room when I say please take good care of yourself, we all want you back in that white hot spotlight, you're OUR piano man.”

“And we're always in the mood for your melodies. And we all hope you're feeling all right! We Love You, the kids, me and an arena or two,” she concluded.

Meanwhile, Alexa, their daughter, also voiced support and love for her father in a separate lengthy note where she reminded Billy Joel, "We love you and we got you, Pop! I just wanted to thank you all for the beautiful outpouring of love and support amid the recent news of my father's health diagnosis."