Travolta posted a short but heartfelt message on Instagram saying: "My dearest Jetty, I miss you more than words can say. I think about you everyday. Happy Birthday. Love, your Dad."
Jett died in 2009 in the Bahamas after hitting his head on a bath while having a seizure. He was autistic, suffered from seizures and had a rare condition called Kawasaki Syndrome, where the wall of the arteries become inflamed.
In 2014 Travolta told US Weekly he didn't know if he would make it through the grief of losing his son.
