It's a big screen adaptation of Stephenie Meyer's latest novel with the same name. Irons is working with Ronan for the first time in the film.
"From the first moment I met her in London, I knew it was going to be easy. Some people are just easy to work with," femalefirst.co.uk quoted Irons as saying.
"You can't define her charm it's just there it's all there, everything. She is always spot-on and perfectly informed," he added.
"It still amazes me that she was 17 when we shot the film. I worked most closely with her and with William Hurt, two masters of their craft, and both were so humble, patient and generous. I listened and learned a lot from Hurt, he is a master," said Irons.
"The Host" is the latest Meyer novel to be adapted for the big screen and it sees back in the director's chair. It is set to release March 29.