Boswell met him in Brunswick on August 8, 1764, and described him as "a brave, worthy, amiable young man". They spent some time together on the next day, talking about religion and melancholy (depression) in the palace gardens.

On October 15, 1764, Boswell sent him a letter from Rippach in Saxony, asking him to send him a range of mint silver coins from Brunswick, as “[i]n all the countries where I travel, I wish to make a collectionof the silver coins struck in the year that I was there”.