The chairman of the London Legacy Development Corporation, owners of the London Stadium, has resigned.
David Edmonds, who has been a director of the company that controls the Olympic Park since 2009, offered his resignation to London Mayor Sadiq Khan last night.
It comes after Sky News learned that the taxpayer-funded cost of turning the Olympic Stadium into the new home of West Ham United has risen from £272m to £323m.
Mr Khan has launched an investigation into the cost and said "big questions" need to be asked about the conversion.
"David (Edmonds) has made an enormous contribution to the legacy of the London 2012 Games and he has helped to steer the organisation through some extremely challenging issues," said David Goldstone, chief executive of the London Legacy Development Corporation.
"We thank him for all his hard work and wish him well in the future."
One of the factors behind the rise in costs is the estimated annual outlay of moving "retractable" seats, Sky News learned.
The cost of the seats, installed to improve the view for football, has increased from an estimated £300,000 to as much as £8m.
Engineers have said work to move them could take 15 days at the end of the football season and 15 days to put them back after the summer - three times as long as the five days initially predicted for each period.
The seating issue threatens the viability of the stadium's summer schedule, which includes concerts as well as athletics in 2017, and could even delay West Ham's return for the start of the new football season.
The rise in the cost of converting the arena for football takes the total cost of the stadium to £752m, all of which has been met by the taxpayer apart from a £15m contribution from West Ham.
London Mayor Sadiq Khan told Sky News he wanted to avoid a "knee-jerk" conclusion on how the cost spiralled out of control, but added that "nobody was in favour of such a large amount of taxpayers' money ... being spent on the conversion."
He said: "Nobody knew, least of all me as the mayor, that the annual cost of would be between £7m and £8m a year for these retractable seats, and there are big questions that need to be asked about how poor decisions were made and what we do going forward."