Nathan claims being in a band with his singer sibling often resulted in explosive arguments due to their ''brutal honesty'' with each other and he's even thrown punches with the lead singer during a squabble over a babe.
Nathan - who is also joined in the group by his brother Jared and cousin Matthew - told ShortList magazine: '' I remember we had a blow out one night over a girl. She was the last girl in the bar, and me and Caleb had made up in our minds that she was going home with one of us, and it became a competition. Next thing you know me and him start fighting, the girl leaves and we carried on fighting.
''We had a big photo shoot the next day, and in the photo my glasses are super-glued together, Caleb is wearing sunglasses with make-up on underneath - it was just like the funniest s**t. The next day we were like, 'What were we even fighting about?''
Nathan admits that being in a band with his relatives can be difficult on occasions but one of the benefits is the honesty they have.
The 34-year-old musician - who is now married to singer/songwriter Jessie Baylin - explained: ''We're so close we can tell when someone is lying. The eyebrow will go up and they'll be like 'Bull-s**t!' We don't ever treat each other with kid gloves. This is my brother so I'll tell him if he's p***ing me off. ''
Kings of Leon are gearing up for the release of their sixth studio album, 'Mechanical Bull', on September 23.