The £80m loan was taken out by property developer Nick Candy from bank Credit Suisse on the One Hyde Park establishment, The Times has reported.
The top floor home is valued at an estimated £160m according to Land Registry figures, potentially making it the most valuable apartment in the country.
Land Registry records show the penthouse is owned by PHB London Holdings Limited and PHB London Dormant Limited, both based in Guernsey.
One Hyde Park was a joint venture between Nick Candy and his brother Christian, and a property company owned by the Qatar prime minister.
The development was formally opened in January 2011 and has consistently seen some of Britain’s most expensive residential homes – however it has also seen one of its apartments worth £5.25m repossessed.
Christian Candy’s CPC Group previously owned specialist lender Fortwell Capital, but a management buy-out was completed in April.
At the time of the buy-out Fortwell had lent around £1.2bn since its formation in 2011.