Heath Ledger 'may have been bipolar'

Heath Ledger may have been suffering from bipolar disorder, a new book has claimed.

The 28-year-old Dark Knight star was found dead in a Manhattan hotel room in January. An autopsy later concluded that the cause was an accidental overdose of prescription medication.

New book Heath: A Family’s Tale, written by English journalist Janet Fife-Yeomans, has raised the possibility that Ledger was suffering from bipolar disorder, as he reportedly showed signs of a number of symptoms, including mood swings.

The breakdown of Ledger's relationship with Michelle Williams may also have been a factor in the onset of the disorder, it is alleged.

Yeomans also suggested that mental illness runs in his family, and interviewed his uncle Haydn Ledger, who was recently diagnosed with the condition.

"I don’t mind people knowing I have bipolar disorder and it’s a shame that it took this long to be diagnosed," he told her.