By Tom Gillespie @TomGillespie1
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The powerful big cat was spotted devouring the young animal in Tarangire National Park in Tanzania.
Though it is common for lions to kills cubs when they take over a pride, shocking acts of cannibalism like this are rarely photographed.
It is unclear whether or not the male's grisly snack was its own young.
British wildlife Photographer Paul Joynton-Hicks MBE captured the harrowing scene on September 5 while taking a client on a private safari.
The 44-year-old said: "We had just had our picnic breakfast and were driving back to camp, past Silale Swamp.
"We stopped the car when I saw the two lions, male and female.
"Our initial thought was that they were a mating couple as we couldn't see any other lions around, and when they mate they take themselves off.
"So we were watching them for a minute or so until I noticed the male was eating.
"While we were watching them we saw the male pulling with his teeth and then the lion cub’s paw flicked into the air.
"That's when we realised he was eating the dead cub."
The scene is so rare that lion expert Professor Craig Packer has never seen another instance, despite having written more than 100 scientific articles about the animals.
Professor Packer, director of the University of Minnesota's lion research centre, said: "Sounds like the male recently entered the female's pride and killed her cub.
"This is the only time we've ever seen cannibalism of small cubs by males.
"Mothers sometimes find the carcasses of their cubs that had just been killed by incoming males, and they, too, will eat the cubs in that context.
"This is the most common context of cannibalism in lions, presumably because these are otherwise healthy cubs that are unlikely to carry dangerous pathogens that might be hazardous to the cannibals."
Paul, who was raised in East Sussex in the UK, has lived and worked in East Africa for 22 years.
He added: "This is the first time I have felt unsettled by a wildlife encounter.
"It felt like the lion was doing something wrong, and yet how can it? It's nature working.
"There is no shortage of food so he wasn't hungry, and he wasn't eating it in the normal greedy fashion, he was sort of picking, pulling, chewing and swallowing.
"Almost just to make a point that he is the boss. There is some reason he was eating that cub, certainly not hunger. Who are we to say what’s right or wrong?
"It was without a doubt the most extraordinary thing I have ever witnessed of wildlife behaviour and at the same time the most abhorrent.
"As we got a little bit closer, he jumped at the female and she moved off.
"He then picked up the dead cub and moved away a little bit. He stopped and ate some more then picked it up again and moved off into the bush."