UPDATE: His 'Sir' title is perfectly apt as Sir Elton John is officially cast in Kingsman: The Golden Circle.
The Rocket man posted a picture to his Twitter to confirm the news. The poster is accessorised with a pair of sunglasses suited to Elton's eyes only;

It's been a long time since Tommy..... #Kingsman

A photo posted by Elton John (@eltonjohn) on May 16, 2016 at 1:24pm PDT

We are more than excited to see what Elton will bring to the cast. Hopefully his fashion flair foremost with some villainy to boast!

Seems an unlikely figure to cast to say the least but then again, we were pleasantly surprised by gentleman Colin Firth's ability to unleash his unadulterated assassination skills. Who says Sir Elton John couldn't do the same?
It was first reported by The Hollywood Reporter and no official comment has been made yet but we would be very intrigued to see what John could bring to the cast. Could he be a major mafia Boss? An ally to the forces of The Kingsman? Or is it a cameo as his good self? It's anyone's guess.
What is known is that Taron Egerton and Mark Strong are back to reprise their roles as Eggsy and Merlin. This time however, they are at the peril of the malicious Poppy (played by Julianne Moore). Matthew Vaughan will remain as director with Jane Goldman helping out with the script.
Kingsman: The Golden Circle is expected for release in June 2017.