The authenticity of an iconic stovepipe hat believed to have been worn by Abraham Lincoln is being called into question.

The leaders of the Springfield-based Abraham Lincoln Presidential Library and Museum cannot explain how a farmer acquired the stovepipe hat more than 150 years ago.

The news comes on the heels of a significant historical gaffe revealing that a famous portrait of Abraham Lincoln's wife that hung in the governor's mansion in Springfield for more than three decades was a fake.

No one has been able to refute the hat's authenticity with certainty. Museum officials say the hat belonged to Lincoln.

The heirloom is valued at $6.5 million.