Prince Harry and Meghan Markle are bound to respond "aggressively" to dad Thomas Markle's threat to bring them to court over his inability to see his grandchildren, a relationship expert has claimed.

Meghan's estranged dad Thomas said in an interview with Fox News that we was ready to go to court in order to finally be able to meet his Archie, two, and Lilibet, who was born in June.

The former Hollywood lighting director, who Meghan hasn't seen since before her wedding to Harry in 2018, said he intended to petition Californian courts for his "right to see my grandchildren in the very near future".

Harry and Meghan with newborn Archie
Meghan hasn't seen her dad since before she got married to Harry in 2018

She told the Sun Online: "The Sussexes are likely to respond aggressively with legal paperwork back, if and when Mr Markle files his officially with the court of California.

In the interview to Fox News, Mr Markle also pleaded with the Queen to allow Lili to be baptised by the Church of England.

Amid a rift between the Sussexes and the rest of the royal family, the relationships expert said Harry and Meghan "won’t appreciate him sticking his nose in and asking the Queen to accept Lily into the church through the media."

The relationship between the Sussexes and other senior royals has been tense ever since the couple dramatically announced they were quitting their lives as senior royals last year to move to the US.

Thomas Markle
Meghan's estranged dad Thomas threatened to petition Californian courts for his 'right to see my grandchildren'

Relations worsened after Harry, 36, and Meghan gave a bombshell interview to US chat star Oprah Winfrey, during which they accused the royal family of, among other things, racism as they claimed "concerns" were raised over how dark Archie's skin tone would be.

During the tell-all chat aired in March, they also alleged The Firm had failed to support Meghan when she felt suicidal while pregnant with Archie.

The interview from their £11m mansion in Montecito, Santa Barbara, was then followed up with a string of high-profile interviews where Harry described the struggles of royal life, which he on one occasion compared to The Truman Show.

The Duke of Sussex also recently announced he was working on releasing a memoir of his time in the royal family by early 2022.

According to Prince Harry, his book will be a first-hand account of his life that's "accurate and wholly truthful".

And it's promised that it will share his "adventures, losses, and life lessons".

However, it is unclear exactly what will be included in the book - although it may well shed new light on why he and Meghan quit the Firm to move to the US.