An official release of The Black Album had in fact often been discussed between Warner Bros. and Prince. In 1991 the record company had wanted to release some type of hits collection to avoid over-saturating the market with an album of new music after the disappointing sales of Graffiti Bridge; plans were for The Black Album to be one CD of a two-CD set, presumably as some way to entice fans to buy the compilation.
Warners instigated the 1994 release as a way for Prince to fulfill part of his contractual obligations. The initial deal required the record company to pay Prince $4 million upfront for the release of The Black Album in November 1994 and The Gold Experience in early 1995; Prince would also be required to record a soundtrack to a to-be-determined Warner Bros. film. This three-album deal would count as two albums toward the remaining four on Prince's infamous “$100 million contract” from 1992.
In fact, Prince's attorney was on his way to Warners to pick up the check and sign off on the paperwork when he received a phone call that Prince had had a a last-minute change of mind, apparently wanting more money. The attorney tried to talk Prince out of his new demands, urged him to take this deal since it was a good one and that Warners wouldn't increase their offer, but his objections were fruitless. The deal was cancelled and Prince's lawyer quit a week later. Prince then hired a 28-year-old New York attorney named L. Londell McMillan, his ninth since signing with Warners in the late 1970s.
A release is secured
At that same time Warner Bros. Records top management was experiencing some upheaval, causing Lenny Waronker and Mo Ostin to leave the firm and restricting their power to make deal. However, they managed to salvage some of the proposed deal, with Prince getting paid approximately $1 million in exchange for the release of The Black Album. This didn't mean that Prince was all that happy with its release; his publicist Karen Lee informed reporters that he was "spiritually against" the album.
No singles were released, but to promote the album Warners had a video made for "When 2 R In Love"; it was completely black and had the song's lyrics displayed as crude subtitles. In advertisement the company offered an "amnesty offer" to bootleg owners: the first 1,000 people to send in their bootleg copies of the album would receive new copies of the album. In Warners' Burbank headquarters employees wore black clothes and cut the lights for a 15-minute black-out on the day of release.
The contents of this answer have been sourced from now-defunct Swedish Prince fan-club Uptown's excellent and long out-of-print 2004 book Days Of Wild: The Definitive Guide to the Musical World of Prince, specifically the entries for 25 October 1994 and 22 November 1994 in the section "Days Of Wild: The Chronology".