Is there a single word for the meaning of the phrase "unlikely but true"? [closed]

I am writing a formal letter and I am looking for a single word that represents or means "unlikely but true."

The context is that I want to reference a story in a book written by my recipient that fits this description of "unlikely but true."

Solution 1:

Improbable carries this sense, but needs to be used judiciously as it is of course not the default sense:

... [also]

unlikely but real or true

• The team made an improbable comeback.

[Merriam-Webster]

• Christina Strutt is seated at her battered kitchen table, wearing an improbable pink floral pinafore ...

[The Times: Interiors; 2010]