Born in
Regensburg, Appl has two older brothers, with whom he sang as a chorister with the
Regensburger Domspatzen, the boys' choir at the
Regensburg Cathedral, performing in concerts across Europe and Asia. Following secondary school, rather than spending a compulsory year in the army he completed his alternative community service working for the
Bayerischer Blinden- und Sehbehindertenbund in Regensburg, providing assistance to blind people in the community. He started training as a bank clerk at the
Liga Bank in Regensburg. He then studied
business administration at the
University of Regensburg, graduating in 2009 with a diploma. His diploma thesis, an empirical study of withdrawn
initial public offerings, received the highest possible marks. He was awarded a scholarship from the
Studienstiftung des deutschen Volkes between 2007 and 2012. While studying for his management diploma, he auditioned at the
Musikhochschule Augsburg for the soloist class taught by
Edith Wiens. Under her tutelage, he continued his vocal training from 2008 at the
Hochschule für Musik und Theater München, and at the opera class at
Bayerische Theaterakademie August Everding, based at the
Prinzregententheater. He also participated in
Helmut Deutsch's
Lieder class. In 2009, Appl met
Dietrich Fischer-Dieskau at a public masterclass of the
Schubertiade in
Schwarzenberg, Austria, which led to his receiving private lessons as his last student until Fischer-Dieskau's death in May 2012. In 2010, Appl moved to London to study singing at the
Guildhall School of Music and Drama with
Rudolf Piernay, intending to study part-time while improving his English, before returning to a career in business in Germany after one year. However, he states that "London was quite life-changing", and he "made contact with great management companies, with Wigmore Hall, with some conductors" while still getting offers to return to the bank, but although "it was tempting to return to a safe haven", he eventually decided to pursue his vocal career. During this time, he attended masterclasses with
Brigitte Fassbaender,
Gerald Finley,
Christian Gerhaher,
Thomas Hampson, and
Peter Schreier, among others. In 2019, he became a British citizen. ==Recitals==