Sarah Matthews, of Dolphin Zone, who confirmed the July sighting of the Vega pod, said it was “quite an elusive pair that appears to pop up randomly in different places” and they had never been seen either with calves or other orcas.
The species typically inhabits the Strait of Gibraltar in winter.
Jay Cowen from the wildlife trust added: “This third orca is kind of perfect because it is so mysterious, as this pod of orca often is.
“I’m really hoping it’s a brand new individual never seen before.”