Neil Diamond & Barbra Streisand
You don't bring me flowers (1978)
This collaboration took place after a DJ merged/mixed the individual recordings by each artist and played the new version on the radio. There was such a demand for the doctored version that the record companies brought the two artists into the studio and recorded an actual duet version. This new recording went to #1 on the Billboard charts and the live version the two sang on the Grammy Award program the following year has been shown for years.