During a 10-week trial at London's High Court which started in January, Harry and the other claimants said dozens of stories about them published by Associated Newspapers in the Daily Mail and its sister title, the Mail on Sunday, from the 1990s to 2011 were based on information which had been obtained unlawfully.
This activity, allegedly carried out by private investigators on journalists' behalf, included hacking into messages on mobile phones, tapping landlines, and eliciting personal information, such as medical records, by "blagging" - deceiving people into handing over confidential details.
Joining King Charles' younger son and John in bringing the lawsuit are the singer's husband David Furnish, actors Liz Hurley and Sadie Frost, campaigner Doreen Lawrence and former British MP Simon Hughes.
Giving evidence, Mail chiefs admitted there might have been some very minor unlawful data law breaches at the papers, such as obtaining phone numbers which were not publicly listed, but said they had banned any use of investigators from 2007.
The ruling by judge Matthew Nicklin is expected to be handed down on July 7.
The stakes for both sides are high. The legal teams estimate the costs of the case will run into tens of millions of pounds, a tab which the losing side will mainly have to pay, while, should the claimants win, they could also expect substantial damages.
Then there is the question of what defeat would mean to the reputations of the Duke of Sussex and the other well-known claimants, or to the titles - among the most widely read in the English-speaking world - and its senior editors and journalists.
