NEW YORK - Madonna was 35 and Tupac Shakur was 22 when they dated between 1993 and 1994. Now a letter from the rapper - which is up for auction - has revealed why they separated.

"For you to be seen with a black man wouldn't in any way jeopardise your career, if anything it would make you seem that much more open and exciting," ABC News cited him as writing.

"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," he added.

Shakur was shot and killed in 1996.

The starting bid for the letter has been set at US$100,000 (S$138,000).