Grohl has been a short term replacement for the Chelsea Lately show and during an interview with Elton it was made public.
The Foo Fighters' main man, currently drumming on the new QOTSA record, admitted that the pair had recently recorded together, "something that people wouldn't imagine the two of us doing together."
Elton went on to confirm the QOTSA collaboration saying it came at a weird time.
"Engelbert Humperdinck had written me a very sweet letter and asked me to sing a duet with him," he explained. "He is part of my history and I couldn't say no so I went and recorded a song with him. Then I drove three blocks and went from Engelbert to Queens Of The Stone Age."
The juxtapostition "was a bit of a mindfuck" Elton added.