Mystery plant

I've just found this mystery plant in one of my raised beds. I thought it was going to be a runner or French bean that had self-seeded from last year, but when I dug it up it looks more like a parsnip root. I've potted it up and will keep an eye on it to see what it turns into!

PS It's looking more and more like a bean of some sort

PPS Turned out to be a runner bean and produced loads of beans