The melon-headed whale/routh-toothed dolphin cross represents the first ever documented offspring of the two species.
As reported in the Independent, researchers from the Cascadia Research Collective found the animal near the island of Kauai last year, according to a report released by the researchers this week.
The individual was seen swimming with another melon-headed whale, with the second animal thought to potentially be the hybrid's mother.
Speaking to Fox News, project leader Robin Baird said: "Hybrids among different species of whales and dolphins have previously been recorded but this is first case of a hybrid between these two species."
Baird pointed to the "morphological characteristics" as the reason researchers decided to take a sample, and DNA anaylsis subsequently confirmd the finding.
Melon-headed whales are actually blackfish and a member of the dolphin family, and genetic analysis suggests the individual was most likely fathered by a routh-toothed dolphin to a melon-headed whale mother.
Baird went on to say that the chances of finding the animal again were unlikely but the team would be returning to try again. He said: "If we find it again, we'd like to try and get a biopsy sample of the melon-headed whale it was associated with as well as get underwater footage [and[ images to better assess morphology."
ORCA have previously recorded sightings of animals thought to be hybrids of common dolphin and striped dolphin in European waters during crossings of the Bay of Biscay.