With his stunning four-octave vocal range and natural vibrato, Freddie Mercury was one of the greatest singers in the history of rock music.

A talented songwriter, the British musician wrote a number of hits for his rock band, Queen, including Bohemian Rhapsody, Killer Queen and We Are the Champions.

But up until this day in 1991, his fans had no idea how sick he was.

Mercury, Queen’s flamboyant lead vocalist, had privately been suffering health complications related to HIV/AIDS.

Unbeknown to the public, the charismatic rock star was diagnosed in 1987, when the HIV/AIDS epidemic was rapidly spreading, but had continued to record with Queen.

HIV (human immunodeficiency virus) can be transmitted through blood that can occur during unprotected sex and sharing of syringes.

Queen band members in 1973: From left,  drummer Roger Taylor, singer Freddie Mercury, guitarist Brian May, and bassist John Deacon. Photo: Getty

Anyone can get it, but in the 80s and 90s the virus was known to disproportionately affect gay and bisexual men.

If left untreated, HIV can turn into AIDS (acquired immune deficiency syndrome), which stops your body from being able to fight off infections.

That’s when you know you’re in trouble.

Freddie Mercury in 1973. Photo: Getty

From 1981 to 1995, tens of thousands of people were being diagnosed with AIDS – and sadly, Mercury was one of them.

On this day in 1991, the 45-year-old singer shocked the world by confirming he had AIDS.

He died the next day.

In 1992, a tribute concert was held at Wembley Stadium in his honour, and in 2018 a biopic titled Bohemian Rhapsody hit cinemas, with actor Rami Malek playing Mercury.