The royal test Princess Diana had to pass before she could marry Prince Charles

The royal test that Princess Diana had to pass before she could marry Prince Charles has been revealed.

• Princess Diana had to pass a special royal test before she was allowed to marry Prince Charles.
• The Balmoral test has been depicted in series 4 of The Crown on Netflix and shows Diana's initiation into royal life.
• This royal news comes after Prince Harry made a surprise appearance on Strictly Come Dancing and left fans thrilled.

The challenge is known as The Balmoral Test and has been referred to by royal experts as an initiation into life in The Firm.

As the name suggests, the test takes place at the Balmoral estate, where the Queen spends her summer breaks.

The process is documented in series 4 of The Crown, which dropped on Netflix yesterday.

The smash hit royal drama depicts the early days of Prince Charles and Princess Diana's meeting, including her trip to Balmoral where her hunting and etiquette skills were put to the test.

Tobias Menzies, who plays Prince Philip in The Crown, revealed details of the initiation that the cast played out in series 4.

Speaking to Cosmopolitan, he said Diana was "being tested through this prism of the strange etiquette and rules, slightly unreadable, of this family".

"Diana gets it and therefore passes with flying colours, a big part of why that relationship is championed by the family going forward," he added.

Meanwhile, royal commentator Richard Fitzwilliams told the Express, "An invitation to Balmoral is traditionally part of the initiation into the Royal Family."

At the time of his comments, Meghan Markle was set to visit Balmoral alongside Prince Harry, after being introduced to the Queen at the castle the previous year.

Fitzwilliams said he expected Meghan to have a “highly successful visit” owing to her “excellent” relationship with the Queen.

"Harry, after all, reportedly introduced Meghan to the Queen at Balmoral last September," he continued.