I think you will find it's not a mortgage! It 's an interest free loan to the club. The stadium will open up fully paid to the contractors.
If the club are not able to repay Bloom in 2023 then he will convert the loan outstanding into shares. Extremely generous and he has said the stadium is a legacy from him to his kids and supporters kids.
Sorry, I meant to say it operates like a mortgage, which is a large loan e.g. it's credit with interest to pay.
What part of interest free do you not understand