This is taken from Frederick the Great's early journals:
"I admire [Voltaire's] eyes, so clear and piercing... I would kiss his eloquent lips, 100 times."
This came as something of a surprise to Voltaire when he found out, particularly considering Voltaire was, at that time, madly in love with Emilie du Chatelet, a renowed physicist. They were on the outs at the time of the trip because Emilie was actually much smarter than Voltaire, which had sent Voltaire into a passion when they discovered it (Emilie placed above Voltaire in an essay contest for the Academie des Sciences).
Fortunately, though Frederick the Great wrote that most evenings he and his court full of young men "lost money at cards, danced till we fell; whispered in each other's ears, and when that had shifted to love, began other delicious moves", Voltaire talked about Emilie a great deal and was off the hook.
Less fortunately, he was still irritated with Emilie for being smarter and his name-dropping turned to mocking quips and compaints about her, which Did Not Amuse Emilie when word got back to her.