Beyonce Knowles' sister Solange suffers from attention deficit disorder (ADD).

The singer admits she didn't believe her doctor when she was first diagnosed with the condition and went back to get a second opinion. ADD sufferers are said to have shortened attention spans and experience difficulty concentrating for long periods of time.

Knowles tells British magazine NME, "I was diagnosed with ADD twice. I didn't believe the first doctor who told me and I had a whole theory that ADD was just something they invented to make you pay for medicine. But then the second doctor told me I had it. I was in denial. I don't understand exactly what it is. The symptoms seem to apply to everyone around me in the industry. Loss of memory, starting something and not finishing it."

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(This news article provided by World Entertainment News Network)