Architect Gareth (42) is a member of the Belfast Photo Imaging Club, and is more used to taking pictures of buildings than kings of the jungle.
Speaking to the Belfast Telegraph last night, he revealed how he captured the shot chosen as overall winner of the competition, which has been running for 33 years.
"I took the image during feeding time at the zoo. That's when the lions are at their most lively," he said.
"I was positioned outside the lion enclosure, with the keeper next to me. We were chatting away about the lions, and as we talked, Fidda the lioness started padding towards us.
"She stopped her head to take a drink, and I spotted her reflection as she began to lap at the water. I thought it would make a nice shot."
Another of Gareth's photos won a 'highly commended' prize.
"It was taken just about 30 seconds after the one of the lioness," he said.
"I think I got lucky! It's brilliant. It's a really good feeling to be a winner."
Gareth said he had dedicated the image to his parents, Anne and Francie.
Although he's only been photographing for five years, Gareth also won the Belfast Zoo photo competition in 2013.
Remarkably, despite his obvious prowess, wildlife photography is not one of his main photographic interests.
"I started out doing pictures of buildings - architectural photography," he said.
"Being an architect myself, that's my main thing."
He took up photography five years ago, after watching professional lensmen take pictures of buildings.
"I reckoned I could do better," he laughed.
"But I do love going up to the zoo, looking to capture something different."
Gareth said that photographing the lions can be very challenging.
"They are photographed a lot, so it can be difficult to get something fresh, get a shot that no else has got before," he said.
"But this year Fidda gave me something different - an intimate, action shot, looking away from the lens.
"She didn't seem to know that I was taking a photo of her.
"It was a very candid shot, almost like street photography."
The Belfast Zoo competition is sponsored by HB and challenges budding and amateur photographers to creatively photograph the animals and scenes of the zoo, capturing the wonder of nature, exhibiting photographic excellence, displaying high quality skills - and a great eye for a photo.