The superstar was diagnosed with the disease in the 1980s, but didn't go public with it until just 24 hours before his death from AIDS-related pneumonia in 1991, reports mirror.co.uk.
Mercury kept his health struggles private for years, but after his death, his bandmate Brian May shared the full extent of his torment.
Back in 2017, May confirmed Mercury has lost most of his foot as his health declined.
Speaking to The Sunday Times, he said: "The problem was actually his foot, and tragically there was very little left of it. Once, he showed it to us at dinner. And he said, 'Oh Brian, I'm sorry I've upset you by showing you that".
"And I said, 'I'm not upset, Freddie, except to realise you have to put up with all this terrible pain'."
May went on to claim Mercury may have survived if had been able to access new AIDS treatments that hit the market shortly after his death.
Mercury spent the last two years of his life in almost complete seclusion, only seeing close friends and family who visited him at his London home.
His final appearance on camera was in a music video for the band's track "These Are The Days Of Our Lives" in May 1991.
He is seen looking frail and gaunt, and was shot from the waist up so his damanged foot was never in seen.
The group knew about his health crisis, but he'd actually told their manager Jim Beach before his bandmates.
"Freddie told me that he was HIV-positive before he told the band," Beach said in the 2011 BBC Queen documentary.
He added: "And this put me in a very difficult position, because he told me he didn't want me to tell the band. So there was I, managing a band, knowing something obviously of crucial importance to the band, which I couldn't pass on to them."
Six months after filming, on November 24 1991, Mercury died at home having succumbed to a bout of bronchial pneumonia.
( With inputs from IANS )