Why William and Kate only appeared at one official charity engagement with Harry and Meghan

When Prince William and Kate Middleton appeared onstage with Prince Harry and Meghan Markle in 2018 to announce that they would be joining forces for the Royal Foundation, the two couples were quickly labelled 'the fab four'.

However, news of a rumoured rift between Kate and Meghan - as well as reports of a 'feud' between William and Harry - soon began to circulate, and it became the only time that the four royals appeared together for an official charity engagement.

In her new book The Palace Papers: Inside the House of Windsor—the Truth and the Turmoil, author Tina Brown wrote about William's concerns over Meghan settling into royal life and why Harry wanted to marry so quickly.

She also details why the Cambridges and Sussexes weren't seen working together in public again in the same capacity.

She writes: 'With blithe proprietorship, she deployed an issue that was not even on the foundation’s docket—women’s empowerment, then at its fervid height with the acceleration of the #MeToo movement.

'"Women don’t need to find a voice. They have a voice. They need to feel empowered to use it," Meghan quotably exhorted as Harry looked on with awe and his brother and Kate stood by with expressionless irritation.'

According to Brown, Meghan 'fluently' took much of the air time and that it created an 'awkward dynamic'.

She continued: 'When it was Kate’s moment to speak, she was strikingly less articulate, as well as brief. Few knew that it was she—after years of providing emotional support to her younger brother, James, as he struggled with clinical depression—who had been the prime mover of the foundation’s mental health campaign.

'It was crafted after careful consultation with mental health professionals, policy experts, and Palace advisers. Now, here was Meghan championing a fashionable cause anointed by Hollywood and sure to make headlines. It was an awkward dynamic. It was later decided the Fab Four would not play onstage together as a band again.'

The Palace has not commented on the claims.