Keith Richards has once again opened up about his tenuous relationship with Mick Jagger and says they "don't know where they stand with each other."

The guitarist spoke with a U.S. radio station about their relationship and said it's an ever-evolving beast.

"I think the relationship is actually still in flux, or still growing — it isn't fixed.

Sometimes he can get up my end, and I have no doubt that I can certainly piss him off sometimes," Richards said.

"At the same time, there's a chemistry between us that we both recognize and that we know works.

In a way, we're both trying to come to terms with each other. Most guys, you know where you stand with.

Mick and I don't quite know how we stand with each other, and we never have."