What is this?

This plant self seeds around the garden. It is huge but as the bees like it I let it grow wherever it wants. But I don't know what it is.

I'd ordered two clematis. One for the new planter and one to replace the one that had died in an existing planter. They arrived today. The extra is one of them.

I had an appointment at the hospital today. I've been taking drugs for my hyperactive thyroid for the last five years. I'm now to stop and they will monitor my blood on a regular basis. However they said that it is highly likely to reoccur. I'll then need to have it removed or take radioactive iodine. I'm not looking forward to either but we'll worry about it if it happens.