London: Pop star Dannii Minogue says she was so ill after giving birth to her first child and feared she had cancer.

The singer-turned-reality TV judge says her weight plummeted and suffered severe tiredness and a bout of appendicitis after son Ethan was born last year, according to reports.

"In my darkest moments I did really worry - because of family history - it could be something that serious. The last year was incredibly tough," she said.

Eventually, Minogue, 37, is diagnosed with an under-active thyroid and receiving treatment for the condition. She's now revealed her fear of cancer after watching her sister, singer Kylie, battle the disease in 2005.

(Agencies)