Liam Hemsworth says Woody Harrelson has the ''heart of a lion and the energy of a 10 year old''.

The Australian actor developed a close friendship with Woody after working with him on 'The Hunger Games' film franchise and Liam has wished the Hollywood star a happy 56th birthday in a tongue-in-cheek message on his Instagram account.

Alongside a photograph of himself and Woody stood together, as well as a series of fruit and vegetable emojis, Liam wrote: ''Happy birthday @woodyharrelson ! You have the heart of a lion and the energy of a 10 year old. I miss ya mate. Stay golden . Here's a whole mess of fruits and veggies for ya (sic)''

Despite their close bond, Woody - who is a vegan and a raw foodist - admitted in 2014 he never knew Liam was the brother of 'Thor' actor Chris Hemsworth.

The quirky Hollywood star only discovered that Liam and Chris are related after an interviewer mentioned the fact while they were promoting 'The Hunger Games'.

Looking surprised and confused, Woody said to Liam: ''Jeez, I never got that was your brother.

''And you do have the same last name, now that I think about it. I honestly never put that together.''

Meanwhile, Woody has also admitted to playing pranks on Liam during the filming of 'The Hunger Games'.

Speaking in 2015, he recalled: ''I did one prank on April Fools' Day where I got our make-up artist to come over to my house and make my face look like I'd been in a bad bike wreck and skidded, blood everywhere.

''I rang [director] Francis Lawrence as I was supposed to film the next day and asked him what I should do. He said, 'First, you need to get to the hospital!'. Then I called Liam and told him to come to the hospital to pick me up, but I made the name up and of course there was no such place.

''That was a dark one, it played on people's sympathies. Nothing good about it, but ...''