p1 := y /. {First[Solve[x^2 + y^2 + x == 1, y, Reals]]}

outputs:

{ConditionalExpression[-Sqrt[1 - x - x^2], 
  1/2 (-1 - Sqrt[5]) < x < 1/2 (-1 + Sqrt[5])]}

I want to get the -Sqrt[1 - x - x^2] out of there and assign it to a variable. I don't care about the conditions, I'm aware of them and need the expression for use out of the Conditional Expression. How do I do that?

I tried list commands combinations (flatten, first..) but they don't work with this.

Am I just supposed to copy-paste?