Brightening a silk shirt

[Absy]

I have a (formerly white) silk shirt, which is no longer as white as it should be due to a stupid washing incident.

Is there anything I can do to return it to its former glory?

If the problem is dye from something else in the wash, then I've had good results with ylon Colour Run - you can get it in the supermarket. You'd have to check if it was ok on silk though.