Back on Dec. 10, during one of Metallica’s intimate fan club shows at the Fillmore in San Francisco, Calif. a magical metal moment went down when original Metallica guitarist and current Megadeth mastermind Dave Mustaine joined his former band onstage for a few songs.

In a recent interview with Powerline, Mustaine talked about the special night and the range of emotions he went through, saying, “I had some mood swings. There was some ups and downs and stuff.” He adds his emotions went from excitement to impatience but all ended up on a high note. "That was really fun," he remarks. "I know a lot of people were really surprised because they never saw me play with the band."

Both Metallica and Megadeth have moved on from playing clubs to much larger establishments, but Mustaine said he enjoyed the off the cuff atmosphere of playing in a small venue. He explained: “I would have liked to have had my sound just so and make sure when I did the solos they would jump up the volume and stuff like that that I’m used to, but we were at a club and playing at a club and playing like a club band. It was fun to take off all the rules and regulations and stuff and kind of shoot from the hip.”

The songs that Mustaine played with Metallica, made sense to him, and he considered them really important. ‘Jump in the Fire’ was the first song he ever brought to the band and ‘Phantom Lord’ and ‘Metal Militia’ were songs he brought to them, as well, so it made sense that they played those songs together and not others.

Mustaine admitted that playing on stage with Hefield again “stirred some of those old feelings up,” explaining, “Me and James, we were like the the Toxic Twins back when we played together and we were a very very dangerous duo.”

As for the consensus on the night overall? Mustaine said it quite simply, “I know I was having fun. I had a smile that I went to bed with.”

Check out Dave's full interview with Powerline here.