The pair have had a fractious relationship ever since Mustaine was sacked by Metallica in 1983.
But following his throat cancer diagnosis, Mustaine said Hetfield was one of the first people to get in contact.
He told Rolling Stone: “A lot [of support] came from people that I knew but I didn’t know cared. Most notably, I got a text message back from my old brother, James Hetfield, and I was so, so happy to hear from him.
“Contrary to what anybody says and contrary to any of the act that we put on, I love James and I know that James loves me and cares about me. You can see that when the moment of truth is here and I’m telling the world that I’ve got a life-threatening disease. Who comes to stand next to me? James.”
Mustaine also spoke about the moment he was first diagnosed. “I was on tour, and I just had some dental work done when I was at home. My teeth are really, really, really sensitive, because I’m a redhead … It just felt like something was wrong in my tooth area,” he explained.
The frontman continued: “So I see the oral surgeon, and he was such a cock. I was in the chair, and he looks at me and then he takes off. And I’m sitting there, and I’m waiting and waiting and waiting, and he comes back in and he goes, ‘It looks like the Big C. You need to go see an ear, nose, and throat doctor.’ I was just stunned with his bedside manner; he was just such a dick.”
Bandmate David Ellefson recently confirmed that Mustaine had completed his treatment for throat cancer and that the band were “hopeful and optimistic” he would make a full recovery.
Mustaine has now added: “I thought about every single trick that I had learned about healing my body and the things I’d learned from martial arts, and I did everything that the doctor said to a T, and hopefully this is the end of it and I never hear of it again. But I feel great.”
Meanwhile, Metallica will headline five major US festivals next year between May and October.