GST liability

SANDHYA SHINGTE (PARTNER) (57 Points)

03 June 2018  
An individual registered under service tax was receiving rental income.
Not registered under GST in anticipation rental income wont exceed Rs. 20 lacs.
But in the month of Dec 17 Rental income exceeded Rs.20 lacs . An individual was registered under GST in May 18.

whether he can charge GST and recover from tenant for Dec 17 to Apr 18?

Whether he has to pay GST liability with interest for Dec 17 to Apr 18?
How to show this in return