Publishers of the Mail on Sunday have agreed to pay “financial remedies” to the Duchess of Sussex, three years after she began a protracted privacy battle over a handwritten letter to her estranged father.

On Sunday, the newspaper printed a statement at the bottom of its front page telling its readers that the duchess had won her legal case for copyright infringement against Associated Newspapers for articles published in the Mail on Sunday and posted on Mail Online.

On page three it ran a 64-word news story stating it had infringed copyright and that “financial remedies have been agreed.” The story was also published on the Mail Online website at 11.58pm on Christmas Day with links to judgments made by courts.

The duchess sued Associated Newspapers over five articles reproducing extracts from a “personal and private” letter to Thomas Markle in August 2018. She won her case earlier this year when the high court judge Lord Justice Warby gave summary judgment in her favour without the need for a trial.

Associated Newspapers appealed on the grounds that the case should have gone to trial. That appeal was dismissed earlier this month by court of appeal judges Sir Geoffrey Vos, Dame Victoria Sharp and Lord Justice Bean.

They ruled that the duchess had a “reasonable expectation” of privacy regarding the contents of the letter. “Those contents were personal, private and not matters of legitimate public interest,” Vos said.

Afterwards the duchess called for a reshaping of the tabloid industry and spoke of how she had been patient in the face of “deception, intimidation, and calculated attacks”.

In her statement, she said: “This is a victory not just for me, but for anyone who has ever felt scared to stand up for what’s right. While this win is precedent-setting, what matters most is that we are now collectively brave enough to reshape a tabloid industry that conditions people to be cruel, and profits from the lies and pain that they create.

“From day one, I have treated this lawsuit as an important measure of right versus wrong. The defendant has treated it as a game with no rules. The longer they dragged it out, the more they could twist facts and manipulate the public (even during the appeal itself), making a straightforward case extraordinarily convoluted in order to generate more headlines and sell more newspapers – a model that rewards chaos above truth.

“In the nearly three years since this began, I have been patient in the face of deception, intimidation, and calculated attacks. Today, the courts ruled in my favour – again – cementing that the Mail on Sunday, owned by Lord Jonathan Rothermere, has broken the law. The courts have held the defendant to account, and my hope is that we all begin to do the same. Because as far removed as it may seem from your personal life, it’s not.

“Tomorrow it could be you. These harmful practices don’t happen once in a blue moon – they are a daily fail that divide us, and we all deserve better.”

Associated Newspapers said at the time that it was “very disappointed” by the ruling and an appeal to the supreme court was being considered.

The duchess’s costs had been estimated at £1.5m before the appeal, but that figure will have increased with the appeal.

The Mail on Sunday and Mail Online statement publication had been ordered by Lord Justice Warby earlier this year. In March he agreed that the font size could be smaller than that asked for by the duchess.

Representatives of Associated Newspapers and the Duchess of Sussex have been approached for comment.