chelsea clinton, ian klaus

After a wild 15-month romance, Chelsea Clinton has called off her planned summer wedding to her Oxford University beau Ian Klaus.

Chelsea's decision to cool her relationship with the American student came after a frightening pregnancy scare that left her in tears and made her come to the painful realization that she wasn't ready for marriage -- or motherhood.

The issue that goes on sale Friday details Chelsea's pregnancy crisis, her booze-soaked relationship with Ian … and more.