In a short memoir appearing in The Musical Times in 1898, Joseph Joachim reminisced fondly about his relationship with Mendelssohn, who, the violinist recalled,

Mendelssohn had met the twelve-year-old violin prodigy around the middle of 1843, and promptly began addressing him alternatim as “Posaunenengel” (trombone cherub) and “Teufelsbraten” (devil's brat). For the next four years until Mendelssohn's death in 1847, the composer mentored the young musician, introducing him to Leipzig and Berlin audiences, as well as taking Joachim under his wing in England (where a special dispensation allowed the child prodigy to perform Beethoven's Violin Concerto at the Philharmonic Concerts in London in 1844) and encouraging him to compose.

Available now for the first time in a comprehensive twelve-volume edition, Mendelssohn's correspondence points to approximately post-June 1843 as the time when he first met the young prodigy, though another source from 1856 advances that event to the later months of 1842. In Beth-El: Ehrentempel verdienter ungarischer Israeliten, released by Ignaz Reich, we read of the eleven-year-old Joachim's participation in a musical Fest in Leipzig, organized by Mendelssohn, in which he kissed the boy on his forehead, a Weihekuss seemingly recalling a similar occasion when, a few decades earlier, Beethoven had reportedly encountered the young Franz Liszt in Vienna. Here we quote from Reich's account of Mendelssohn's introduction to Joachim: