The Shadowland writer penned the long-running title prior to current scribe Peter Milligan.
"Hellblazer fans," Diggle wrote on Twitter. "Various HB creators are doing a... thing... in London on April 23. More details once it's officially announced."
Many writers and artists who have worked on the comic have been British, including Diggle, Milligan, Mike Carey, Garth Ennis, Warren Ellis, Steve Dillon and Jamie Delano.