Plant ID

This plant was found growing amongst my onions in my raised bed. I found it in a part that has been used by squirrels to hide  their walnuts.

One of these said walnuts sprouted because when I pulled it out it was still attached and growing from a walnut shell.

I would love to grow a walnut tree and am hoping desperately that this is a walnut and so I carefully pulled it out and re-potted it.

Do i hope in vain?