Prince Harry will reveal the details of a sensational row between Meghan and Kate in his new book, the Mail has learned.

During the run up to the Sussexes’ wedding in May 2018, Harry writes that Meghan told Kate that she must have ‘baby brain because of her hormones’.

Kate, who gave birth to her third child, Prince Louis, a month before Meghan and Harry’s wedding, was understandably upset by the accusation.

But Meghan also became offended because she was reprimanded for her comments.

During the run up to Harry and Meghan’s wedding in May 2018, Harry writes that Meghan told Kate that she must have ‘baby brain because of her hormones’

Harry says that Meghan was told she wasn’t close enough to Kate to make such remarks about her hormones.

A well-placed source said: ‘In the book Harry says that there was a discussion about the timing of the wedding rehearsal and the flower girl dresses and Kate was very upset.

‘Meghan said that Kate must have ”baby brain” because of her hormones.

‘It caused a huge row because Meghan was told that she wasn’t close enough to her sister-in-law to discuss her hormones and it wasn’t the way people spoke to each other within the Royal Family.

‘The book makes clear that Meghan felt the fall-out wasn’t her fault, but it doesn’t exactly make her look very good either.’

In an extraordinary development, Harry – who reveals that the brothers called each other ‘Harold and Willy’ – details the extent of the rift between the brothers.

Using language in the book that appears designed to shock, Harry describes his brother as ‘my Archnemesis’.

Meghan, Harry, William and Kate watching a fly-past to mark the centenary of the Royal Air Force in 2018 

The detail about the fight between the women, however, gives the fullest account yet about how the bitter rift extended to their wives.

Meghan first discussed the row with Kate during her interview with Oprah Winfrey two years ago.

Spare is published on Tuesday 

When Oprah asked if reports were true that she had made Kate cry, Meghan replied saying ‘the reverse happened’, adding: ‘It made me cry and it really hurt my feelings. It was a really hard week of the wedding and she was upset about something but she owned it and she apologised.’

Harry will reveal that the brothers had countless physical fights from childhood upwards.

One of the worst in recent years was over the way in which William shared his views on Meghan.

A source said: ‘Harry doesn’t hold back on William, He writes that Harry told him: “Meg is difficult, she’s rude, she’s abrasive. She’s been rude to the staff.”

‘Harry says that William called him names, that he wanted Harry to agree with him but that he became enraged when Harry “had the audacity not to follow the script”. William grabbed him by the collar, ripping his necklace and pushed him to the floor.’

More allegations look set to emerge not only from the book but during a third television interview, the Mail has learned.

Meghan being interviewed during her and Harry’s recent Netflix documentary  

As well as television appearances with Anderson Cooper in the US and Tom Bradby for Britain’s ITV, Harry has granted another interview to broadcaster and former American football player Michael Strahan.

The 90-minute interview with Strahan is expected to be broadcast on US television early next week to coincide with Tuesday’s book launch. 

A source said: ‘There will be many more revelations and discussion about the book so the Royal Family will want to brace themselves.’