According to Australia's Daily Telegraph newspaper, 76-year-old Janelle was admitted to the Royal North Shore hospital (RNSH)

with suspected heart problems.

The publication reports that Janelle was under observation after being admitted Thursday afternoon, but has now been discharged.

"Janelle was taken to hospital last week but has since been taken home," a source told the newspaper. "Her daughter Antonia is home here and with her, but it wasn’t a mercy dash, she was already home.

"They are of course concerned, but if it was anything super serious, Nicole would have been home straight away."

The Daily Telegraph adds that Janelle has been struggling following the death of her husband Dr Antony Kidman in September 2014. After suffering a heart attack at the Tanglin Club in Singapore, he was taken to Tan Tock Seng Hospital, where he later died.

Following her father's death, Nicole credited husband Keith Urban for helping her through the difficult time.

"When you have your partner who just literally carries you through a tough time - he’s been amazing to me," she said during an interview on The Ellen Degeneres Show. "To have my husband just step up that way, it makes me cry. He’s amazing. ... We all go through hard times in our lives, but to be literally carried by your partner, and physically at times because I was so devastated. I'll do anything for that man."

Nicole's former brother-in-law Angus Hawley, the ex-husband of her sister Antonia, also died of a heart attack in April, 2015, aged just 46.

After Angus' death, his brother David told Daily Mail Australia: "It's a real shock, he was one of the fittest men I've ever met – he's swimming everyday."

Angus had four children with Antonia.