This is one of those documentaries that feels like it directs itself, so improbable is its story: The Peckham-born Catholic and heavyweight boxing promoter formerly known as Frank Maloney finally acknowledges the gender confusion that has dogged her life and, in her early 60s, transitions to becoming Kellie. In particular, the scenes where Maloney builds up to telling each of her three children that she is a woman play out in strange parallel to the succession of bouts we previously see her client Lennox Lewis undergo chasing the world title. There are similar undertones of destiny too. “This journey is not one that you choose, this journey chooses you,” Maloney says just before her crucial reassignment surgery. Where Knock Out Blonde is not so sharp is the way it digs into the childhood roots of Maloney’s discomfort. Perhaps it’s the kind of thing that can never be delineated, but it’s not fully clear how this brew of identity, sexuality and self-image contributed to Maloney, a pugilist who didn’t make the cut, finding herself managing Lewis at the apex of the macho and hyper-capitalist 1990s boxing world. In much of the footage, she looks glum; ground down by the kind of inner denial or furtiveness that saw her sneaking off to a transgender salon in Staten Island as Lewis was preparing for his first fight with Evander Holyfield at Madison Square Garden. When Maloney comes out as Kellie in the mid-2010s, in her need for validation she showed a worrying addiction to the rapacious publicity circuit that she mined during her promoting career: tabloid front covers and appearing in the 2014 season of Celebrity Big Brother. This film feels like a fundamentally healthier endeavour and, given its authorised nature, stays admirably honest about the emotional damage in the vicinity. Maloney’s second wife Tracey, the biggest victim of Kellie’s middle-aged attempts to shore up her identity as “Frank”, is unsurprisingly still angry, if understanding. Her three daughters also air their ambivalence; they continue to call her “Dad”. Knock Out Blonde begins to overstretch itself as it proselytises for the transgender cause; the less obtrusive cheerleading works better, such as Kellie resuming promoting with female boxers, or her hardman brother Eugene coming round after at first contemplating “killing” her. It’s only true misstep, though, are some fussy stylised dramatisations: clumsy but understandable trying to flesh out the mysteries of gender, downright distasteful when rendering the particulars of the 2009 suicide of her client Darren Sutherland. But watching Maloney fight her way from this shady and taciturn demi-monde to her current softer, expressive reality is miraculous and moving. Knock Out Blonde: The Kellie Maloney Story is available on the Icon Film Channel on 5 August and on digital platforms from 7 October.