Tupac Shakur dumped Madonna because she's white.

The late rapper - who died 21 years ago when he was shot six times in a drive-by shooting - dated the 'Like a Virgin' hitmaker for three years before his death and has admitted in a gripping letter he penned when he was in prison that he ended their secret relationship because of their different cultures and how his ''people'' would react.

He wrote at the time: ''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. 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.(sic)''

Although he called it quits with the 58-year-old singer, he claimed in his letter that he never meant to ''hurt'' her and offered out his hand for a possible friendship.

He explained: ''I never meant to hurt you. As you can see I have grown both spiritually and mentally. It no longer matters how I'm perceived.

''Please understand my previous position as that of a young man with limited experience with a extremely famous sex symbol.

''I offer my friendship once again time this time much stronger and focused. If you are still interested I would like to further discuss this with you but some it couldn't wait. I felt compelled to tell you... just in case anything happened to 2 me.''

The letter is set to go up for auction between July 19 and July 29 at Gotta Roll, according to TMZ, and the bids will start at $100,000.

Following her relationship with Tupac, Madonna went on to have daughter Lourdes, 20, with ex-partner Carlos Leon, son Rocco, 16, with her ex-husband Guy Ritchie, and adopted four children; David, 11, Mercy, 11, Stelle and Estere, four.