April 29, 1945 - March 16, 1970: Age 24
If you can hear music in your head when you read the title, "Ain't No Mountain High Enough", the female side of the duet is Tammi Terrell. She was a soul singer, and her big break was singing an album's worth of duets with Marvin Gaye. (Since the song is probably already playing in your head, here it is on YouTube.)
In October 1967 she was doing a concert with Gaye when she collapsed on stage. When she was taken to hospital, it was discovered she had a brain tumour. It was malignant, and her health deteriorated from that point on until she died in March 1970. Rumours were that her condition was caused, or worsened, by domestic abuse on the part of both her current boyfriend and her previous one. There were also rumours that she was having an affair with Gaye, but she was not. They were, however, very close friends, and Terrell's death threw Gaye into a two-year depression during which he didn't perform in concert. During that period, he produced the album "What's Going On", a significant step forward in maturity and depth from his previous work. Check it out here, it's a nine-minute version and worth every beautiful second.