John Travolta pays sweet tribute to his late son Jett on what would've been his 28th birthday

Although gone, Jett certainly isn't forgotten.

John Travolta showed the love for his late son on what would have been his 28th birthday on Monday.

The beloved Grease star took to Instagram to share a sweet tribute in his memory.

Posting a beautiful black and white throwback photo of the father-son duo, the 66-year-old actor wrote: "Happy Birthday Jetty! We love you!"

John's wife Kelly Preston also shared a post in honour of Jett, who tragically died 11 years ago.

Kelly - who married the actor in 1991 - posted a snap of herself hugging her son and wrote: "Happy Birthday to our sweetest Jetty, we love you!!"

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Fans offered their condolences to the Travolta family, with one writing: "Happy birthday to your beautiful angel."

Another echoed: "May his memory be a blessing."

Jett tragically died at the age of 16 in 2009 after suffering a seizure on a family vacation to the Bahamas at Christmas.

John later confirmed that his son had autism and would regularly have seizures.

We're sure Jett is smiling down at his dad and the rest of his family!