The missive, dated to January 1995 when the All Eyez on Me musician was in jail facing a sexual assault charge, has been put up for sale by bosses at online auction website Gotta Have Rock and Roll.
In the letter, Tupac wrote that he ended his relationship with Madonna because he was worried that dating a pop megastar would disappoint old friends and fans in the gangster rap scene.
"For you to be seen with a black man wouldn't in any way jeopardize your career, if anything it would make you seem that much more open and exciting," stated the handwritten note, which has been obtained by TMZ.com editors. "But for me at least in my previous perception I felt due to my 'image' I would be letting down half of the people who made me what I thought I was. I never meant to hurt you."
Tupac, who began a relationship with Madonna after they met at the 1993 Soul Train Music Awards, also apologised for verbally lashing out at her after she made comments in an interview about dating rappers.
"Those words cut me deep seeing as I had never known you to be with any rappers besides myself. It was at that moment out of hurt & a natural instinct to strike back and defend my heart & ego that I said a lot of things (sic)".
Explaining that he had grown "spiritually and mentally" since their split, he added, "Please understand my position as a young man with limited experience with an extremely famous sex symbol."
After going over the rights and wrongs of their relationship, Tupac ended the letter by offering his famous ex-girlfriend his friendship and warned her to "be careful".
The letter is up for sale from 19 to 28 July (17), with bids starting at $100,000 (R1 340 000).
Tupac died following a drive-by shooting in Las Vegas in September 1996.
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