Oxalic acid ("wood bleach" in DIY-type shops) bath - a fork could fit in a wall-paper tray.
Put it in and leave it for a day - rust gone.

Dry and clean it well as soon as it comes out, and give the raw metal a wipe with a light oil to keep the rust from starting again, which it WILL DO and it this case right away.
Or paint the metal right away - if later remember to remove whatever you used to keep it bright.