CHICAGO - When a United Airlines flight attendant met bass player Marvin Isley on a plane 20 years ago, she immediately told her co-workers he was going to become her husband. And she was right.

Sheila Isley said the Isley Brothers' youngest sibling always acted like she had the high-profile job in the relationship, not him, and treated her as if she were flying the planes.

"That's the kind of person Marvin was," she said. "He was a straight-up, standup guy."

Marvin Isley died Sunday morning of diabetes at an inpatient hospice at Weiss Memorial Hospital in Chicago. He was 56.

He had battled diabetes for decades, losing his legs to the disease in 1997.

Marvin Isley stopped performing in 1996 after his diabetes caused him to have a stroke. He lost the use of his left hand and doctors had to amputate his legs.

He joined his brothers' band in 1973. By that time, the Isley Brothers had established themselves with hits like 1959's "Shout," which sold more than 1 million records. Isley splintered off to form Isley-Jasper-Isley in the 1980s and returned to the Isley Brothers in the 1990s. The group was inducted into the Rock and Roll Hall of Fame in 1992.

Longtime R&B record producer and fellow Hall of Famer Leon Huff said Marvin Isley will be missed.

"The Isley Brothers always had a fantastic band and great stage shows, and Marvin played a big part of that," Huff said in a statement. "He really brought the funk. It's a great loss."