Billy Joel marked a rare personal moment as he celebrated his daughter Alexa Ray's milestone 40th birthday 🎉 The 76-year-old “Piano Man” singer was diagnosed with a brain disorder earlier this year, resulting in the cancellation of his tour, but is reportedly in good spirits as he focuses on treatment and recovery. Alexa's mom is Billy's ex-wife Christie Brinkley 💕 #fatherdaughter 📸: #billyjoel