Must I Expand Everything?

Algebra Level 4

$(b+c-a)^3 + (c+a-b)^3 + (a+b-c)^3 - 3(b+c-a)(c+a-b) (a+b-c) \\ = \\ K(a^3 + b^3 + c^3 - 3abc)$

Above shows an algebraic identity for constant $$K$$. Find $$K$$.

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