Princess Ingrid Alexandra of Norway has cut her bachelor's degree at the University of Sydney short as her mother's health worsens.

The Daily Mail understands the 22-year-old has flown out of Australia to return to Norway to be with her family. 

Her mother, Crown Princess Mette-Marit, is 'gravely ill' with pulmonary fibrosis, a debilitating lung condition that makes it difficult to breathe.

Her father, Crown Prince Haakon, has flown home early from his official visit to Japan to be with his wife.

Princess Ingrid Alexandra's grandmother, Queen Sonja, 88, was diagnosed with heart failure last week, making it a difficult time for the Norwegian Royals. 

The 22-year-old moved to Australia to study a Bachelor of Arts at the University of Sydney.

Her degree is focused on international relations and political economy. 

She was seven months into the three-year degree and had been staying at the prestigious St Andrew's College, which costs up to $45,000 a year.  

Her hasty departure comes just days after a man was issued with an apprehended violence order over a 'suspicious' letter that was allegedly sent to the college in Camperdown, where the Norwegian Princess had been staying. 

The alleged letter was intercepted by her security detail.

NSW Police attended the college last week to investigate the incident. 

'NSW Police issued a 63-year-old Glebe man with an apprehended personal violence order following inquiries by officers attached to Inner West Police Area Command,' a spokesperson told the Daily Mail.

'No charges have been laid in relation to this incident.'

The matter has been listed for mention in Newtown Local Court this Wednesday.

Princess Ingrid was spotted departing Sydney on Tuesday.

The royal was flanked by two Sydney Airport workers while walking to the gates.

The Princess has maintained a low profile since beginning her studies in Australia with the Royal House of Norway last year requesting she have a 'normal' university experience.

It's understood she had a 24-hour security team living with her at St Andrew's College.

It is unclear when, or if, Princess Ingrid will return to resume her degree.

The university of Sydney is currently on study break with semester one exams set to start next week.