The flight taking the Queen’s coffin to London was the most tracked in history, according website Flightradar24.
Nearly six million people tried to follow the plane’s route from Edinburgh to RAF Northolt within its first minute in the air, the website said.
The huge traffic caused disruptions to the site, where users can track the path of planes in the air.
More than 4.79 million people watched on its site and app and 296,000 were watching on a YouTube stream, it said.
The previous record was when a flight carrying US politician Nancy Pelosi to Taiwan last month was followed by 2.2 million people on Flightradar24.
The Queen’s coffin was flown on an RAF Globemaster C-17, after lying in state at St Giles’ Cathedral in Edinburgh.
The flight used the callsign “Kittyhawk”, used for any military flight with the Queen on board.
Princess Anne and her husband Sir Timothy Laurence accompanied the coffin, with the princess saying she had felt fortunate to be able to share the final hours of the life of her “dearest mother”.
“It has been an honour and a privilege to accompany her on her final journeys,” she added.
Prime Minister Liz Truss and Defence Secretary Ben Wallace were among those waiting at RAF Northolt for the flight, which landed just before 19:00 BST.
Flightradar24 said it had taken steps to make its platform as stable as possible before the plane took off.
The flight to Taiwan taken by Ms Pelosi, the US House of Representatives Speaker, in August attracted interest as she was the highest-ranking American official in 25 years to visit Taiwan, which China sees as a breakaway province.
Explaining how Tuesday’s figures had dwarfed that traffic, Flightradar24 said: “Based on our experience last month, we expected a large influx of users, but this immediate, massive spike was beyond what we had anticipated.”
It said about 600,000 users were able to “successfully follow the flight before performance degraded”.
“Even though our platform suffered under such heavy load, Queen Elizabeth II’s final flight from Edinburgh to RAF Northolt is by far the all-time most tracked flight on Flightradar24 and will likely remain at the top for a long while,” it said.
The RAF C-17 carrying Queen Elizabeth II’s coffin is beginning its descent toward London.
— Flightradar24 (@flightradar24) September 13, 2022