Blackwell claims the R's offered him the chance to move to Loftus Road at the end of the 2008-09 campaign, only to rebuff the suggestion.
Blackwell was sacked just two games into the new Championship season following a 3-0 defeat at the hands of Neil Warnock's side.
"It didn't help that it was Neil," Blackwell said of his departure.
"It's ironic. There's no doubt that Neil has had a big influence on my career playing-wise, coaching wise... and now getting the sack as well. He's done everything for me!
"This time last year I could have gone to Queens Park Rangers straight after the play-off final and the club turned it down.
"Neil rang me on two occasions and said: 'I've spoken to Flavio Briatore and they did want you to come here'. But I had a contract and I felt I should honour it at Sheffield United.
"That's why I stayed there. It's ironic that Neil takes the job on and has now got the money to move it forward. That happens in football."