A humpback whale seen swimming in the River Thames over the weekend has died.
The mammal was spotted lying motionless on mudflats along the River Thames at Greenhithe on Tuesday afternoon.
Sam Lipman, from the British Divers Marine Life Rescue (BDMLR), said the death was "not wholly unexpected".
BDMLR said the whale, seen surfacing off Greenhithe on Sunday, was "definitely a humpback" and was probably lost but did not appear to be in any distress.
"It's really sad to find a humpback whale like this, deceased," Ms Lipman said.
"As the days were going on, we were seeing more photos of its condition, we were starting to realise that maybe it wasn't in the greatest of health.
"I think we weren't expecting this to happen so soon and we were hoping it wasn't going to happen at all," she added.
The BDMLR had said the creature likely arrived because of a navigational error, possibly during the recent high spring tides.
A year ago "Benny the beluga" spent about three months in the busy waterway.
On Sunday, a group of volunteers had observed the mammal surfacing repeatedly over a three-hour period.
A Port of London Authority (PLA) spokesman said people who had seen it had estimated it was five or 10 metres in length.
Postings on social media have been mourning the humpback's death.