No! GDPR is about personal data, which is well defined in the regulations and does not include blog posts. The right to delete data (or "be forgotten") is nothing to do with GDPR.
If the original post contained personal data, it is a different issue but if that was put out into the public domain, it is a hard problem to solve.
No, if you intentionally made that data public then it's done. GDPR doesn't, say, force you to remove political views of Theresa May from newspapers, despite that being covered by personal data, because Theresa May made those views public.
