Lokks like a Lupin in the foreground? I think it is also a form of Epilobium it is so close you won't have planted it next to your lupin therefore it will have seeded there.
I have worked as a Gardener for 24 years. My latest garden is a new build garden on heavy clay.
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https://www.wildlifetrusts.org/wildlife-explorer/wildflowers/great-willowherb
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.