A funeral for Justin Christopher Gatto was held at Richmond's St Ignatius' Catholic Church on Friday, attended by hundreds of mourners .
He died on October 30 - four days after his 34th birthday - after falling from a central Melbourne apartment block.
"With your happy smile, and sense of fun, we can't believe that you are gone," read a written tribute handed to mourners.
"You brought so much joy to every life you touched and you are missed, so very much.
"But, a beautiful soul lives on forever and memories of you we will always treasure."
The message, titled Missing You, also reads rest in peace, "free from all pain".
Mick Gatto arrived at the service dressed in a black suit, white shirt with a light blue, gold and black tie, his face hidden by designer sunglasses.
Among the hundreds of people gathered at St Ignatius' Church were underworld figure Toby Mitchell and construction union boss John Setka.
The funeral service began with Louis Armstrong's What A Wonderful World.
Mick and Justin's siblings Damien and Sarah are expected to read a eulogy.
The closed silver coffin with gold details is expected to be taken out of the church to the song Over The Rainbow by Israel Kamakawiwo'ole.
Mourners were asked to donate to mental health organisation Headspace "in line with Justin's wishes".
A private burial with family will follow the service.
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Australian Associated Press