Redevelopment of property

Hi My father had purchased a flat (condo) in an Apartment building for a total consideration of INR 1 Lac in Pune in 1983. 2 years ago, all the owners of the block of condos got together and commissioned a builder to redevelop the flats. At that time, the value of the flat was around INR 70-80 Lacs. During the redevelopment, all tenants received a sum of INR15K per month as compensation during redevelopment. After the redevelopment was complete, the redeveloped area was handed back to the owners in February 2017. The area is similar to the one that was given up (ie the size of the flat prior to redevelopment) and no money changed hands (other than the redevelopment compensation mentioned above). The property as handed over is valued at INR 1 Cr. My father has been advised that he needs to pay long-term capital gains tax on the valuation of the flat, less the adjusted value of the purchase price. Is that so? If so, how should the taxable value be calculated and when is the tax due? If my father sells the flat in April 2017, is there any additional tax liability and what would that be?