It's 8 pm and I am sitting in an edit suite in Soho, London, watching the uncut rushes of Freddie Mercury's infamous birthday party in Munich, 1985. I am lucky enough to be directing a new documentary about my hero.

The film is so clear that I feel that I'm at the party myself. I can taste the champagne, hear the music and smell the PVC. Beneath the disco balls and ultraviolet lighting, amongst the fun, the leather, bare buttocks, moustaches, strippers and Brian May dressed as a witch – is Freddie. It is hard to tell if he is enjoying himself or not. A three-tiered cake is carried across the dance floor by several chefs as the birthday boy is ushered over to blow out the 39 candles. Slightly embarrassed, he blows out a few and retreats into a corner of the room away from everyone, where he spends most of the night.

This is man who performed "I Want To Break Free' in drag in front of 350,000 fans at the Rock In Rio Festival. The man who sang 'Bohemian Rhapsody' upside-down with the Royal Ballet. The man who stole the show at Live Aid with the whole world watching. Yet being the centre of attention at his own party appears to make him squirm.

Freddie Mercury said he was a man of extremes. On stage he was indestructible. He was Mr Fahrenheit. Off stage he was shy, witty and, according to everyone close to him, the best friend you could ever have. Freddie Mercury was the Great Pretender.

This party footage in the past has often been used to depict his "outrageous' personal life. However this wasn't really Freddie's personal life. It's what he wanted us to believe was his personal life, to embellish the image and persona he had created.

Freddie's personal life was very different. Yes he had his fair share of crazy nights out and he was not afraid to admit he was excessive in all areas, but Freddie was also someone who would go to the ballet, the opera and musicals. He collected Japanese art and Koi carp. He was a loyal godfather, rang his cats when he was away from home, played Scrabble and his favourite TV show was Countdown.

The real significance of the party was that it was to be the last of its kind. It marked Freddie's farewell to the lifestyle he had been living for five or so years. Freddie was almost forty, the world had woken up to AIDS and things had to change.

From 1979 to 1985, Queen had gone from being the biggest band in Europe to the biggest band in the world. Freddie was living it up in New York and Munich, away from the prying eyes of the British press, where he could be himself. During this time Freddie recorded his first solo album Mr Bad Guy. Despite receiving a large advance from CBS the album failed to make an impact, reaching No. 6 in the UK and 159 in the USA. Walter Yetnikoff, Head of CBS, claimed it was the worst record deal he had ever made.

After that party in Munich, Freddie returned to familiar territory, Queen and London. He moved into his dream mansion and the band began work on A Kind Of Magic which would be Queen's first UK number one album in six years, followed by their record breaking Magic Tour which ended at Knebworth Park in August 1986.

The band decided to take another long break, but already Freddie was itching to do something new. He was now 40 and wanted a challenge in life. Unfazed by the disappointment of his first solo outing, he was determined to make something "of some note. Not just another bunch of songs,” as he put it. He thought about writing a musical and then had the idea of recording an album of cover versions, starting with "The Great Pretender'. However, that went out of the window when he got a call from one of the world's greatest opera singers.

Flash back six years. It's 1981. Freddie and his personal assistant Peter "Phoebe' Freestone are sitting in the Royal Opera House, Covent Garden watching Pavarotti in Verdi's Un Ballo De Maschera. Freddie loved Pavarotti's voice and admired his control but then the mezzo-soprano walked on and Freddie was blown away. His jaw dropped and he turned to Peter and said "I have just heard the most beautiful voice in the world". That voice belonged to Montserrat Caballé. Freddie was in awe. Years later on tour with Queen in Barcelona, he was interviewed on TV, and when asked who his favourite singer was he beamed, "You won't believe this but it's Montserrat Caballé "She's just the best!"

When news got back to Montserrat, she invited Freddie to Barcelona to meet. Not only did she agree to record a song, but an entire album. Freddie was in his element. He was working with his heroine and stretching his musical skills into a new dimension. On an emotional level he had finally found happiness with long-term boyfriend Jim Hutton, who had now moved into Garden Lodge. Life couldn't have been better, except Freddie knew he was HIV positive – he had AIDS. He didn't know how long he had to live but what he did know was that the current album he was working on with Montserrat could be his last and he was determined to make it the best.

The critically acclaimed "Barcelona' single, and album, went on to sell over a million copies and became the official song for the Barcelona '92 Olympic Games. Freddie regrouped with Queen and went back into the studio to record two more albums in quick succession, The Miracle and Innuendo, completing a fraction of the third, Made In Heaven, which the band released in 1995. Freddie was more creative than ever, fuelled by the determination to make great music that would last forever.

Ten days before Freddie died, Jim Beach, the band's manager, met with him to discuss what could be done with his legacy. Freddie quipped, "You can do whatever you like with my image, my music, remix it, re-release it, whatever "just never make me boring".

Over the years Jim Beach and the remaining members of Queen have continued to keep that promise and in 2012, to celebrate 25 years of Barcelona, the whole album was re-recorded the way it should have been "had Freddie had the balls to do it at the time.” The Eighties keyboard has been replaced with an eighty piece orchestra which lifts what was already an outstanding album into a whole new stratosphere. Rousing, triumphant, emotional and magnificent.

Freddie Mercury continues to capture the hearts, the minds and the ears of everyone who hears his music or watches his videos and concerts. He hated interviews but when he had the right person asking the questions – someone he could trust – he was utterly open, modest, hilarious and charming. Life was for living. Life was for fun. "Fuck tomorrow, it's today, dear".

Twenty-one years after his death, Freddie Mercury is still very much alive. He influences and enlightens new generations of musicians and fans alike. He will always be unique. He will always be the greatest and he will never, ever be boring.

And now I want to cry.

Rhys Thomas, London, May 2012.