After Blowfly was revealed to be Aussie icon Shannon Noll on Monday, Osher tweeted he knew it was the Australian Idol runner-up while the show was still airing in other states.
"I don't see the clues, I can't hear the voices when they're singing as I'm not standing near a speaker – but I KNEW it was Shannon two eps ago when he tapped me on the shoulder and then poked me in the eye, which is the exact trick he used to do back on Idol," he said.
However, one furious viewer slammed Osher for spoiling the reveal.
"Er... timezone, dude. Rooster has only just finished singing in South Australia," the viewer responded.
Osher hit back with a scathing response, telling the viewer he was not responsible for spoiling the reveal.
"Oh I'm so sorry that I came into your house, unlocked your phone, and forced you to look at an app," he sarcastically replied.
"I won't do it again.
"Also, if you don't know to not look at Twitter when you don't live in an east coast timezone – you probably shouldn't own a phone."
His response divided fans, with some saying the viewer should stay off social media if they want to avoid spoilers while others said Osher's comment was "unprofessional".
"Maybe don't go on social media if you don't want spoilers," a fan commented.
"Can't blame Osher," one said.
"Every time, without a doubt, people still don't know how social media works," a third added.
Others slammed Osher for his response to the viewer, with one telling him to "calm down".
"Very unprofessional response," one said.
"True, but in some vein, maybe you could stay away for a while until everybody gets to see it before commenting on social media? Goes both ways, mate. Common sense and decorum," another commented.
"So those of us not on the east coast shouldn't own a phone – what an arrogant remark ... I've tuned out now," a furious viewer wrote.
Shannon Noll was revealed on Monday, followed by Destiny's Child member Michelle Williams on Tuesday.
Superstar panellist Mel B correctly guessed the Grammy Award-winning singer-songwriter, while Abbie Chatfield thought it was original Destiny’s Child member LeToya Luckett, Chrissie Swan predicted Brandy, and Dave Hughes was certain it was Cyndi Lauper.
Never miss a thing. Sign up to Yahoo Lifestyle’s daily newsletter.
Or if you have a story idea, email us at firstname.lastname@example.org.