I think it's rather Adrian is not interested, especially being in Maiden now. He is also probably writing the 2nd SK album. Remember Bruce said in an interview from recent years that Adrian likes more the hard rock stuff than Bruce's heavy and down tuning approach. Expected. Roy's reason must have happened just now (I doubt it's the problem he had during the recordings of the album, the line-up was revealed a while ago; maybe it's something else) and I think his relationship with Bruce will remain the same. I wonder if not having Roy on the tour will reflect for future solo tours. I hope not. It's a massive blow, although Bruce is the main face for the fans. And they can't cancel the tour, not now. I think it will be fine and well received with more or less the random band. But if there are shows next year too (as rumored, by Bruce too), he can participate. The interest to the current tour might drop a little because Roy is an integral part of Bruce's career and sound.
A few days ago Roy shared this photo and I thought this would be the guitar he will be using during the tour (he recorded the new album with a Les Paul iirc). Beautiful silver Les Paul and he looks good on this photo.
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I can't imagine Dave playing for any band other than Maiden.
The style is probably not his favorite, but he liked AOB, according to Bruce.