City bosses shelled out more than £7.5m to take control of the company responsible for regenerating parts of Sunderland, including the Vaux site and Seaburn.
Siglion was set up in 2014 as a partnership between Sunderland City Council and stricken construction giant Carillion.
But, following last week's confirmation council chiefs had taken sole charge of Siglion, the local authority's accounts have revealed it paid £7,535,000 to do so - or '£6.903m plus taxes'.
"Having started a programme of investments, Siglion is now moving into the next stage of its delivery," said council leader Graeme Miller.
"This is as a fully council owned development company helping to create more a vibrant, dynamic and healthy city, with projects such as the Beam and the seafront Stack.
"This will see Siglion continuing to deliver key regeneration work, including Vaux, Seaburn and Chapelgarth, as well as the management and growth of an investment portfolio of properties.
"Siglion will build upon the momentum achieved to date and help continue our city's regeneration."
But the decision has prompted scepticism from opposition groups, who said it was "impossible" to say whether the deal was a good one.
The city's Liberal Democrats claimed Siglion and its assets were now worth less than when the firm was set up.
And Wearside's Conservative group added any decision about the Vaux site would be treated with "utmost caution and scepticism".
Coun Michael Dixon said: "Whether this is a good financial deal for the council and city residents, is impossible to say at this stage, as the way it was announced left a lot to be desired."
The Siglion purchase was approved by the city council's cabinet on January 30 and "statutory notices in respect of this Cabinet decision were published on the same day", Coun Miller insisted.
He added: "Opposition councillors were notified of the Cabinet proposals and decision, and raised no scrutiny questions at the time.
"Now that the transaction has been concluded they suddenly find a voice to publicly criticise our city's regeneration."
The collapse of Carillion in January 2018 left Siglion without its "development partner" and saw work on the Vaux site grind to a halt.
Construction later restarted with the appointment of Tolent Construction in July last year.
The council's decision to take "full control" of Siglion was completed in March.
This also saw "development manager" Igloo, a regeneration specialist, "exit the partnership".
Unlike the city council and Carillion, Igloo did not hold a stake in Siglion.
According to the council's statement of accounts for 2018/19, Siglion has an "overall current net worth" of £17.437m.
