The trainer triumphed over magician Jamie Raven on Sunday night after wowing viewers with her clever dog Matisse. But it was later revealed that another collie, Chase, had performed the most heart-stopping part of her routine and then been hidden.
TV watchdog Ofcom received 507 complaints from voters believing they were "tricked", while ITV reported another 130.
ITV boss Peter Fincham claimed the decision not to come clean about the use of Chase was a "judgement call" but should have been made clearer, but lead judge Cowell was angrier about the "c**k up" and producers felt his wrath.
"The moment I found out I literally put my head in my hands. I spoke to a lot of people after and I did raise my voice," he told the Daily Mirror. "But it was mainly people owning up to it. They felt embarrassed, they felt frustrated, they felt stupid but you've got to man up to this stuff.
"The producers are absolutely gutted. I was so depressed for the show, for Jules and for the producers themselves because they are not horrible people. They didn't think how it would appear.
"I was frustrated because I didn't really know what I was judging until afterwards so I felt like a bit of an idiot."
Britain's Got Talent 2015 finalists
Britain's Got Talent 2015 finalists
Jules and Matisse wowed the Britain's Got Talent crowd with their comedy dog routines to go on and win Britain's Got Talent 2015
2/10 Calum Scott
Calum Scott was Simon Cowell's Golden Buzzer act earlier in the series and has performed 'Dancing on My Own' and 'We Don't Have To Take Our Clothes Off' so far
3/10 Old Men Grooving
Old Men Grooving are showing Britain's Got Talent that dad-dancing is definitely back in - they went through based on the public vote after the judges' votes were tied
Light dance group UDI offer something 'unique' to Britain's Got Talent - they went through based on the public vote after the judges' votes were tied
5/10 Danny Posthill
Danny Posthill will be hoping his funny impressions of the rich and famous bag him the grand Britain's Got Talent prize
6/10 Jamie Raven
The Britain's Got Talent judges watch contestant Jamie Raven turn fire into ice during a live semi final - he won the public vote
7/10 Isaac Waddington
Isaac Waddington performs in the Britain's Got Talent semi-final to win the public vote and guarantee a spot in the final
8/10 The Neales
Family vocal group The Neales moved Simon Cowell to tears with their semi-final performance of 'Father and Son' to win the judges vote and go through to the final
9/10 Cor Glanaethwy
Welsh choir Cor Glanaethwy perform on Britain's Got Talent before winning the public vote to make it through to the grand final
10/10 Entity Allstars
Alesha Dixon pressed her Golden Buzzer for dance group Entity Allstars and they later progressed into the final courtesy of the judges
Cowell added that no-one had intended to conceal Chase's involvement but regretted the "cloud" that now hangs over O'Dwyer.
"I want people to feel proud of her and that she did well and she should be happy," he said, after the 48-year-old won the £250,000 cash prize and a spot on the Royal Variety Performance line-up.
O'Dwyer has explained that she used Chase for the tightrope stunt because Matisse is scared of heights.
"I was disappointed when people said I allegedly hid Chase and I was trying to make it like Chase was Matisse," she said. "That's not so. I introduced Chase in the semi-final and I said Chase is Matisse's best mate. Why put the pressure on the dog when I already have another dog who can perform it on television?"
However, Chase was not brought out when O'Dwyer and Matisse faced the judges, something Cowell admits "should have happened".
Ofcom is assessing complaints before deciding whether or not to investigate.Reuse content