Music legend Aretha Franklin has written a candid letter to fans after cancelling another show due to health problems.

The 71-year-old singer axed a number of concerts this year (13) so she could receive treatment for an undisclosed illness, but promised she would return to the stage in July (13).

However, the star has now called off her upcoming 27 July (13) show in Clarkston, Michigan, which was rescheduled from a date in June (13), and she apologised to fans in a letter, revealing the gig clashes with her planned treatment schedule.

She writes, "Regretfully I must cancel one last time my... concert July 27 (sic) due to my miscalculation of the end of my treatment. It would be totally disruptive to stop them now and go into concert with total success right at the door, 100 per cent. I love you much and more than the spoken word can tell. I'll see you next summer."