Actor Prakash Raj has joined the cast of filmmaker Mani Ratnam's upcoming multi-starrer film 'Ponniyin Selvan', which also stars Aishwarya Rai Bachchan. "On the sets of Mani Ratnam's Ponniyin Selvan. A journey with the master, which started 25 years back from Iruvar, continues," Prakash tweeted. The film also stars Karthi, Chiyaan Vikram, Aishwarya Lekshmi, Mohan Babu and Jayam Ravi.