The Sei whale, which is rarely seen in Scottish waters, was discovered on Wednesday near North Queensferry in Fife.
Volunteers for the British Divers Marine Life Rescue (BDMLR) found the whale who was half-submerged in chest deep water. At first, they successfully freed the whale, who found its way back into deeper waters and was seen to be “swimming strongly”, as it headed Eastward.
However, the whale sadly re-stranded itself, and its body was found on Thursday at Dalgety Bay.
As of yet, the cause of death of the whale is unknown, however, a necropsy will be performed by Scottish Marine Animal Strandings Scheme, in order to find out if there was any underlying cause.
The body will be cut up and taken to a landfill site.
In a statement, BDMLR said: “Unfortunately the survival rate of large whales who have already stranded is quite low as there is usually a reason for why they have beached themselves."
They described the whales’ death as "a sad ending to what was a hopeful rescue”.
Councillor David Barratt told the Herald: "We seem to be seeing and increase in whales visiting the Forth in recent years.
"I'm told a autopsy will be undertaken and that discussions are underway with the Institute of Biodiversity, Animal Health and Comparative Medicine as the University of Glasgow.
"It will be interesting to see if the death was due to human impact or natural causes.
"It's very sad."