Hasn't he just broken a 'golden rule' regarding prepositions?!

Not hardly. The not-ending-a-sentence-with-a-preposition "rule" was invented out of whole cloth by just one man, John Dryden, for just one reason, he didn't like ending sentences with prepositions. People have been placing prepositions where they fit best for many hundreds of years before or after Mr Dryden elevated his quirky style to a "grammatical rule".

[link and link]

Ceci n'est pas un seing.