NGN, which owns The Sun, was the parent company of the now-defunct and notorious News of the World, which was caught out in a phone-hacking scandal less than a decade ago.
The controversy saw the launch of the Leveson Inquiry, and the closure of the News of the World after more than 160 years in print.
The evidence formed part of a series of court cases which have followed the hacking scandal and subsequent inquiry, and still continue to this day.
After several years of investigations, in July 2011, journalists were found to have hacked the phones of murdered schoolgirl Milly Dowler, relatives of killed British soldiers, as well as victims of the 7/7 bomb attacks in London.
Several members of the royal family were found to have had their phone messages intercepted by the paper.
In 2014, the Old Bailey heard that the Duke and Duchess of Cambridge, as well as Harry, were all victims.
The then-Kate Middleton had her messages hacked 155 times in the space of a few months between 2005 and 2006, including on Christmas Day and Valentine's Day.
William was hacked 35 times, and Harry nine times.
A full public inquiry was announced by then-prime minister David Cameron immediately.
At the end of the 16-month inquiry in November 2012, Lord Leveson delivered a damning verdict on decades of "outrageous" behaviour by newspapers.
The Appeal Court judge called for the establishment of a muscular new independent regulatory body, backed by legislation, with the power to require prominent apologies.
His 2,400-page report pulled no punches in condemning the behaviour of elements within the newspaper industry.
The press had repeatedly acted as if its own code of conduct "simply did not exist", and "wreaked havoc with the lives of innocent people", Lord Leveson said.
In the current lawsuit, claims have been filed on behalf of Prince Harry at the High Court, and it is believed it will go as far back as when he was a teenager with a mobile phone in the early 2000s.
A spokeswoman for NGN said: "We confirm that a claim has been issued by the Duke of Sussex. We have no further comment to make at the current time."
A source at Reach plc, which owns the Mirror, said they were aware that proceedings had been issued but had not yet received them, so they were unable to comment further.
It comes only days after his wife, the Duchess of Sussex, announced she was suing the Mail on Sunday, after it published a private letter she wrote to her father.