Builder asking me to bear capital gains tax

I signed a sale agreement with a builder in Kolkata in 2006 and moved in to the flat in 2008. All payments were completed by then. However I did not register the flat due to my fund problems. The value of the sale agreement is Rs.45 lakhs, the value now as per circle rate (registration value) is Rs.1.20 crores. Now that I am approaching the builder for registration, he is asking me to first compensate him for the capital gains he will have to pay - he claims he will have to pay capital gains tax on the registration value as per notification of 2013. My tax consultant however tells me this was amended in AY 2019-20. Please help.