What would you do if the world's second-largest shark showed up during your Scuba dive?
For divers Gavin Ó Briain and Davy Lynn of UCD Sub-aqua divers, it was a case of keep calm... and keep the camera rolling.
The pair were 20 metres below surface off the Stags of Broadhaven, the rocky islands off Co. Mayo's coast, when the silhouette of a shark appeared in the distance.
The experienced divers were quick to identify a couple of basking sharks, and kept their composure to capture the once-in-a-lifetime video footage.
"At 20 metres I was facing Davy and saw the head of a basking shark arrive behind him," Ó Briain says. "I started to point at it so Davy would know to turn around. There was two of them, they did a couple of loops around us and stayed for a good two minutes."
Growing up to 10m in length, basking shark are the second-largest fish in the ocean after whale shark. They are harmless to humans - literally having no teeth - but are listed by the ICUN as endangered in Irish waters.
The sharks appear off the Irish coastline between April and August (watch more extraordinary footage from Kerry here), where they feed on plankton.
“I’m delighted the divers got to swim with basking sharks," says UCD Sub-Aqua club captain Mehdi Enterzary.
"It can be a bit of shock when an animal as big as a basking shark comes out of the blue, but our divers were very composed and even got some great footage.
"For me it really highlights the high level of training these divers have gotten at UCD Sub-Aqua club and that is equally satisfying.”
"Afterwards, we went up to do our safety stop and of course boast about how good our dive was!" Ó Briain says. "It was without a doubt the most amazing thing I’ve ever seen underwater, and probably in my life."