Naomi Watts wrote a series of love letters to Matthew Mcconaughey to prepare for 'The Sea of Trees'.

The 46-year-old actress - who appears alongside the Hollywood hunk in the drama movie - has revealed she sent Matthew some intimate letters as she prepared to play his wife in the upcoming film.

She shared: ''We didn't have any time to prep [for the movie] so when Matthew reached out to me via email, I said: 'Do you mind if we write to each other in character?' And he wrote back and said: 'Write at will, Joan.'

''So we proceeded to create this relationship through letters. Some would be just a few lines or something fairly benign, and then other times it would be a long letter about how we failed and how we need to change and accusations of giving up; the same old story, your classic marriage problems.''

Naomi said the unusual form of preparation was ''great'' and it helped her to get into character.

She told Vogue Australia magazine: ''Sometimes we would write poetry, sometimes love letters, sometimes stormy letters, sometimes I would leave a voice recording [as Joan] knowing he was going to be shooting in the forest that day. It was great.''