The last image the world has of Ozzy Osbourne on a stage is not of a man diminished by illness, but of a heavy metal sovereign. At Villa Park in Birmingham, on 5 July last year, the 76-year-old frontman of Black Sabbath sat on a black throne crowned with a sculpted bat, surrounded by the original members of the band and a congregation of rock royalty that included Metallica, Guns N’ Roses and Alice in Chains. The concert, titled “Back to the Beginning”, was a homecoming in the city where he was born and where, in a working-class Aston terrace, the dark alchemy of heavy metal first took shape. He sang seated, his body already claimed by Parkinson’s disease, but the voice that once turned doom-laden riffs into a global language held firm.

What the crowd did not know, and what his widow Sharon Osbourne has now disclosed to the BBC on the first anniversary of his death, is that the show almost did not happen. Two weeks before the performance, doctors told Osbourne he was dying and urged him to cancel. “Ozzy knew he was dying,” she said. “They told him, ‘Don’t do the show.’” His reply, she recounted, was characteristically blunt: “Really? Get out of here.” The defiance was not bravado alone. Osbourne was terrified he would not be able to sing, and he was, by his wife’s account, deeply depressed by the knowledge that the end was near. Yet the concert became what she calls “a gift” – a final communion with the audience that had been, in her words, “the greatest love affair of his life”.

That love affair began in the late 1960s, when John Michael Osbourne, a dyslexic, stuttering school-leaver who had worked as a plumber and a slaughterhouse hand, answered an advert for a vocalist and, with Tony Iommi, Geezer Butler and Bill Ward, formed a band that would take its name from a Mario Bava horror film. Black Sabbath’s 1970 debut, with tracks like “Paranoid” and “Iron Man”, did not simply invent a genre; it gave a voice to adolescent alienation and working-class disaffection on an industrial scale. Osbourne’s solo career, launched after his 1979 dismissal from the band, proved equally transformative, and his later incarnation as the bewildered patriarch of MTV’s reality series “The Osbournes” made him an unlikely television icon. Through all the excesses – the bat-biting incident, the substance abuse, the tabloid notoriety – he remained, as Birmingham’s new “Ozzy Day” exhibition frames him, a “Working Class Hero”.

On the anniversary, grief has taken many forms. His daughter Kelly Osbourne posted on Instagram that she mourns not only her father but “the soul I was before death taught my heart its own name”. In Birmingham, the city has laid out a trail of his landmarks, staged orchestral tributes, and placed the very throne from Villa Park inside a commemorative exhibition where fans can leave messages in a book of condolence. Sharon Osbourne, visiting for the first Ozzy Day, wept when asked why she had come. “Because I can’t forget what Birmingham did for Ozzy,” she said. Her message to fans, repeated in interviews from São Paulo to the BBC’s local radio, was the one she says her husband would have wanted: “When you want to remember me, just turn the music up as loud as you can and bang your head.”

It is an instruction that transforms a private ritual of mourning into a collective, defiant noise. In bedrooms, in cars, in clubs, the volume goes up, and for a few minutes the silence that death imposes is broken by the sound of a man who, even as his own body failed, refused to let the music stop.