Thomas Markle claims he kept the letter from his daughter, Meghan, Duchess of Sussex, a secret, until her friends "vilified him" publicly.
Markle, 77, who has been estranged from his daughter since it was revealed that he colluded with the paparazzi before her wedding to Prince Harry, explained that he had never planned to share the letter Meghan sent to him but changed his mind after an article appeared in People magazine.
Speaking in the Court of Appeal this week on behalf of Associated Newspapers Ltd, Andrew Caldecott QC, said: ‘[Mr Markle] had honoured the privacy in this letter until the People article appeared.
"The article painted Meghan in a glowing light, while insisting the negative stories about her were lies. But Mr Markle says Meghan’s decision to reveal the letter left him with no choice but to go public. 'The letter was presented in a way that vilified me and wasn’t true. It was presented as her reaching out and writing a loving letter in the hope of healing the rift but the letter isn’t like that at all.'
"Either we believe in freedom of expression or we do not. Mr Markle has been royally attacked in the People magazine in precisely the way he there describes, and this is his reply."
Meanwhile, Meghan, 40, was forced to issue an apology to the Court of Appeal this week for failing to remember exchanges she'd shared with then-press secretary Jason Knauf about crafting the letter to her estranged father "with the understanding that it could be leaked".
Meghan won a case earlier this year after a summary judgement from Lord Justice Warby ruled the Mail on Sunday's publication of her letter to her father was "manifestly excessive and hence unlawful".
The newspaper's publishers are seeking to overturn the summary decision because they feel the matter should go to trial.
Following this week's three-day hearing, Court of Appeal judges will return their findings in the next few weeks.