In a word, he became the new Charlemagne.
The exaltation of the South German dynasties had long been a favourite project with Napoleon, who saw in the hatred of the House of Bavaria for Austria a sure basis for spreading French influence into the heart of Germany.

Not long after the battle of Austerlitz, the Elector of Bavaria, while out shooting, received from a French courier a letter directed to "Sa Majeste _le Roi_ de Baviere et de Suabe."[63] This letter was despatched six days after a formal request was sent through Duroc, that the Elector would give his daughter Augusta in marriage to Eugene Beauharnais.

The affair had been mooted in October: it was clinched by the victory of Austerlitz; and after Napoleon's arrival at Munich on the last day of the year, the final details were arranged.
The bridegroom was informed of it in the following laconic style: "I have arrived at Munich.

I have arranged your marriage with the Princess Augusta.

It has been announced.