Help with ID

I wanted to identify the purplish plant with alternating leaves. I tried to track this last year and if I remember correctly it doesn't stay purple and becomes shrub/tree like rather than flowering plant. Right now its next to rhubarb under an apple tree. Ultimately wondering if it should stay or go.

Looks Amaranth-y though no real idea.

I also thought it looks a bit like the ornamental-gone-weedy red amaranth that grows around here, But amaranth is, I think, opposite, not alternating. And ours has slightly rounder leaves whereas yours is more pointy.