In a jailhouse letter coming up for auction, the late rapper Tupac Shakur explained to pop star Madonna that the two could not continue their relationship because she was white.

“M. I’ve waited a long time 2 finally write this Mainly because I was struggling to find all the answers so that I wouldn’t leave any unanswered questions,” Shakur wrote in the missive dated Jan. 15, 1995, 4:30 a.m., while he was being held at Rikers Island awaiting sentencing for his Dec. 1, 1994 conviction for sexual abuse. “First and Foremost, I must apologize to you Because like you said I haven’t been the kind of friend I know I am capable of being,” he continued in a partially redacted image of the handwritten letter, which the Manhattan auction house Gotta Have Rock and Roll supplied to TMZ.com.

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“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 & exciting. 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.”

“The person we got it from knew Madonna very well, knew the whole story of that time in her life,” auction-house owner Pete Siegel, who confirmed the letter’s authenticity, told Newsday. The same day Shakur wrote the letter, Vibe magazine journalist Kevin Powell recorded an interview with him in a Rikers conference room.

Madonna, 58, revealed on Howard Stern’s SiriusXM radio show in March 2015 that she had dated Shakur, who was killed in a 1996 shooting at age 25. Recalling her infamous 1994 appearance on CBS’ “Late Show with David Letterman,” she told Stern she had cursed on the late-night talk show because, “I was in a weird mood that day. I was dating Tupac Shakur at the time and the thing is he got me all riled up on life in general. So when I went on the show I was feeling very gangsta.”

The auction preview begins July 12, with bidding from July 19 to 28. The starting bid is $100,000.