Meghan, Duchess of Sussex, forgot about her exchanges with a former aide because her messages were automatically deleted.
The 40-year-old former actress apologised to the Court of Appeal this week for failing to remember exchanged she'd shared with then-press secretary Jason Knauf about 'Finding Freedom' and also crafting a letter to her estranged father Thomas Markle "with the understanding that it could be leaked", and has explained in a statement that Kensington Palace arranged a cyber security expert to set up an automatic deletion system on her phone in 2016.
Meghan explained she hadn't told the court about the contents of the messages - in which she agreed her former employee should meet with Omid Scobie and Carolyn Durand about their book - before because it was Mr. Knauf's job to deal with the media and "his exchanges with these reporters did not stand out as unique".
Her own email searches didn't bring up the exchanges but she would "not have been surprised" by this because "most of our discussions were either in person or via text".
She added: "I was unable to retrieve any text messages with Mr Knauf, because an automatic deletion system had been implemented on my phone by a cyber security specialist brought to Kensington Palace for my devices in 2016. Mr Knauf was aware of this meeting."
Meghan - who has children Archie, two, and Lili, five months, with husband Prince Harry - also claimed the court case hadn't reached the stage of carrying out "any of the extensive and focused searches that would have been required" ahead of a trial, and explained she was under a lot of stress at the time.
She said: "I was in the first trimester of my third pregnancy at the time [having suffered a miscarriage a few months before] and was feeling very unwell.
"My doctor advised me to avoid stress, particularly given the recent miscarriage days after the defendant threatened to break the confidentiality of the original 'sources' for the People magazine article, which resulted in my having to make an urgent application for an anonymity order.
"This was granted by Mr Justice Warby, but I found the process extremely stressful, and it took its toll physically and emotionally."
The former 'Suits' star knew the searches "would be a labour-intensive and invasive exercise" because Associated Newspapers Ltd originally asked for "177 search terms including 'I love you', 'Harry', 'sex scene', 'Doria', 'mother', 'Kate', 'William', 'Suits', 'baptism', 'kiss', 'childcare', 'Archie' and countless others (although these were later narrowed down)."
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.