So the backstory is as follows, I worked at a big company for a long time and quit rather angrily. No harsh words were said, simply demonstrated my disappointment when I was refused a promotion. During my notice period I requested a recommendation letter from my boss about 4 times, to which he said he will get around to it but never did it.
The main reason I left, and why I couldn't stomach waiting with my quitting was because I was denied the promotion I was promised because I was told that I didn't get the promotion because I was hospitalized having surgery during the time that promotions were given. Following my quitting I spoke to a lawyer and attempted to file a law suit, after several hostile back and forth letters we decided to not go to trial. Potential gain (Which in this case would only be the difference in money that the promotion would've granted times the months up until I quit) would've been very little compared to the cost of the trial.
It's all in the past, however now a new potential employer is requesting a detailed recommendation letter (containing responsibilities, tasks etc') which I don't have. I don't feel comfortable now reaching out to my former boss with any request of this nature because despite ending employment on good terms, the following law suit was directed majorly at him.
The question is how to approach the new employer, how to explain the situation of not being able to supply the letter without making him think less of me as an employee, or worse, asking me to confront my previous boss again.