Self seeded ID...

in Plants
this was a tiny seedling who had snuck in to the pot of a nursery bargain bench hydrangea I bought last summer (which is doing great, love a bargain!).
It has now shot up, about 1m high. Any idea what it is, and can I / should I move it? (I have hydrangeas and Lamium in this bed so don't want it to take over if it is worth keeping).
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