Why did Geoffrey Chaucer write The Book of the Duchess?

The
reason why Chaucer wrote The most often is given as a straightforward
explanation. Blanche, the wife of his patron (person who commissioned and paid for poems and
provided livelihood) the Duke of Lancaster, John of Gaunt (son of England's King Edward III and
father of King Henry IV), died (1368) and Chaucer wrote The Duchess
(1368-69) as a memorial to her life and death: he wrote Blanche an
. Yet other scholars find
problems with this explanation.
Firstly, the poem deviates from standard elegy form and devotes
much attention to the virtue and worthiness of the Black Knight, who is recognized as the
representation of John of Gaunt, making the claim of elegy a little less tenable.

Secondly, Chaucer was not a courtier of John of Gaunt but
rather was a courtier and emissary for King Edward III and received an annuity (livelihood
income) from Edward III before his marriage to Philippa who was in service to Edward's Queen
Philippa. While Chaucer...

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