The article says: > One Beethoven biographer63 has previously suggested, on circumstantial grounds, that Ludwig senior may not have been Johann van Beethoven’s

The article says: > One Beethoven biographer63 has previously suggested, on circumstantial grounds, that Ludwig senior may not have been Johann van Beethoven’s biological father > 63 Canisius, C. Beethoven “Sehnsucht und Unruhe in der Musik”: Aspekte zu Leben und Werk Originalausgabe. Schott, 1992 So it's been hypothesized but presumably not demonstrated genetically.