Another, very different example, might be the Czech composer Leoš Janáček whose entire career as a composer was one big Late Efflorescence. Until he met his muse, the much younger (and married) Kamila Stösslová to whom he wrote some seven hundred passionate letters, he was a largely unknown regional composer of dull organ and choral music and folksong arrangements. Nearly all of the works for which he is acclaimed, such as his two string quartets, the Sinfonietta, the Glagolithic Mass and his five late operas, were all written in the last decade of his life, after he had met Kamila.
Janáček's String Quartet No. 2 was given its nickname "Intimate Letters" by the composer himself in a reference to his long correspondence with Kamila. This performance is by the Emerson Quartet and the photo is of Kamila (and her son) in 1917, the year they met.