The most famous sequence in all of wildlife film-making happened 48 years ago. During the filming of Life on Earth – the groundbreaking BBC show that set the blueprint of nature programming as we know it today – David Attenborough crept through the forests of Rwanda, and unexpectedly found himself being playfully set upon by a family of gorillas. As they clambered over him, Attenborough turned to camera and said: “There is more meaning and mutual understanding in exchanging a glance with a gorilla than with any other animal I know.”

Almost half a century on, the sequence still has the power to give you goosebumps. This is possibly why it has formed the backbone of a new documentary. A Gorilla Story is a much starrier affair than its predecessor – it was directed by the Oscar-winning James Reed and boasts Leonardo DiCaprio as an executive producer – but its conceit is fascinating: after all this time, how are those same gorillas doing?

As the film shows, that depends on who you are. If you’re a general conservationist, then this is almost universally good news. Back in the 1970s, Rwanda’s gorillas were being poached almost to the point of extinction, but the conservation work catalysed by Dian Fossey (and, although he’s too modest to admit this, the huge spotlight shone on the animals by Attenborough) means that numbers are almost fully recovered.

But if you’re some of the gorillas themselves, things are a little more complex. The Pablo Group, as the family is known – named after the young gorilla most drawn to Attenborough – finds itself in a state of flux. All the animals Attenborough met have died, and their descendents rule the roost. Gicurasi, the dominant silverback, is growing older. A new challenger by the name of Ubwuzu has noticed this, and now he is throwing his weight about in every possible direction.

Everybody knows that the cardinal sin of watching a wildlife film is to anthropomorphise the animals too much, to map our own human insights and experiences on to animals who do not share them. That said, Ubwuzu is clearly a bit of a prick. He beats up Gicurasi in a show of dominance, then lashes out at a younger gorilla on the verge of adulthood named Imfura, who spends much of the film covered in welts and gashes doled out by Ubwuzu in an effort to keep him in his place.

As Attenborough points out: “Perhaps there are only so many beatings a gorilla can take.” So it’s little wonder that Imfura sneaks back into the family when Ubwuzu is off with his mistress, and kills his baby. Violence, power struggles, grief; this is the stuff of high drama.

Possibly too high drama, in fact, because all of this is crammed into just over an hour of film, which gives the whole thing a sense of whistlestop. When the characterisation of the animals – their personalities, their individual roles in the tight social network of their family – is this beautifully captured, you can’t help but wish it was given the series-length treatment it deserves.

What also works against the film is that all this epic death or glory gorilla footage is in direct competition with what is probably the main draw of the whole thing: David Attenborough.

Attenborough turns 100 in a few weeks, which means that every appearance here automatically feels elegiac. When he reads about the Rwanda encounter from his diaries – for the love of god, someone publish these diaries! – you find yourself overcome by admiration for the man, and his ability to articulate a moment with exactly the right weight.

This reaches its emotional climax when he talks about Pablo, the gorilla who grew up into an unconventionally successful silverback only to be killed while protecting his family from a rival group at the age of 33. For all the (admittedly brilliant) natural footage captured in A Gorilla Story, what will stick in the mind most is the unbearably poignant sight of a near centenarian casting his mind back to a dear old friend and intoning, “I will never forget him.”

Clearly Attenborough has no truck with nostalgia. This is the second new project he’s released in the space of a fortnight, which hints at a preference for forward momentum. But for those of us who grew up with him – which is to say all of us – this feels like one of the last chances we’ll get to sit at the feet of an adored relative.