Posting a snap of the pair together to his 2.1 million followers, Elton gave a nod to their close relationship.
Elton captioned the photo: "Miss you so much. #PrincessDiana."
The post also included a crying face and a heart emoji.
Diana tragically passed away in 1997, with Elton reworking 'Candle In The Wind' to pay tribute at the royal's funeral.