Prince Andrew has officially been financially cut off by the King, marking a new low in relations between the brothers.

An updated biography by acclaimed royal writer Robert Hardman, serialised by the Mail, reveals that despite the Duke of York’s attempts to call the monarch’s bluff, Charles has acted decisively.

In recent weeks he has instructed his Keeper of the Privy Purse, the monarchy’s finance director, to sever his beleaguered younger brother’s annual personal allowance - believed to be in the region of £1 million a year - and no longer pays for his seven-figure private security detail.

‘The duke is no longer a financial burden on the King,’ confirms a source.

The King, who has also long made clear his wish to see Andrew move out of his vast 30-room mansion at Windsor, Royal Lodge, has now placed the ball firmly back in his brother’s court.

In doing so, he has, Hardman also reveals for the first time, made good on his late mother’s determination to solve the ‘Andrew issue‘ once and for all.

Indeed, impeccably placed sources reveal that had she lived another year, Queen Elizabeth, who had long been accused of being reluctant to take action against her rumoured favourite son, would have forced him to leave his family home and downsize to Frogmore Cottage, the former home of the Duke and Duchess of Sussex.

An updated edition of Hardman’s best-selling biography, Charles III: New King. New Court. The Inside Story, which was published earlier this year, is now being brought out in hardback with extra material and three new chapters packed with fascinating detail.

Among the new revelations is how Prince Harry’s determination to doggedly pursue legal action against the Home Office over its decision to withdraw his round-the-clock security when he quit royal duties has driven a wedge between father and son.

The King fears that if he repairs his relationship with Harry he could be dragged into the case, placing him in ‘legal jeopardy’.

Royal insiders have also hit back at suggestions that they failed to help Meghan when she joined the Royal Family, saying she threw their offer back in their faces.

They insist, far from throwing the Duchess to the wolves, as she has suggested, they did everything in their power to help her - and it was she who said no.

Sources say the King is not against some sort of rapprochement with the Sussexes despite the barrage of criticism he had received. But it has not been an easy process.

When Harry returned to the UK in May the two did not meet. The prince was offered a room at Buckingham Palace but instead chose to stay in a hotel.

‘We were told it was for security reasons,’ says a member of the King’s staff. ‘I’m not sure you could get anywhere more secure than the Palace.’

As for Andrew, it can now be revealed that his attempts to play a dangerous game of high-stakes poker over Royal Lodge against his brother have backfired.

Sources close to the Duke of York have long argued that he has a cast-iron, long-term lease on the late Queen Mother’s former home in Windsor Great Park.

Although he no longer undertakes royal duties, has been stripped of his patronages and military associations and is effectively barred from using his HRH title in public over his association with convicted paedophile Jeffrey Epstein, the Duke has been determined to cling to the vestiges of his former life, most notably his home.

He has made clear to the King’s advisers that they have no right to force him to downsize and has firmly rejected suggestions that he move to nearby Frogmore Cottage, which although smaller at five bedrooms, appears adequate for his needs and has the added benefit of being inside the Windsor Castle security ‘ring of steel’.

Now that the King has effectively called his brother’s bluff, Andrew is going to have to find the money for the upkeep of his vast property, as well as his security detail, with no visible sign of independent income.

According to Hardman, this apparently includes the cost of protecting several valuable and historical works of art and pieces of furniture borrowed from the Royal Collection, the treasure trove of antiques held in trust by the monarch on behalf of the nation.

Andrew has repeatedly asserted that he can continue to pay for his own upkeep, claiming to have found ‘other sources of income‘ related to his contacts in international trade, sufficient to cover all his costs. But His Majesty will be watching with interest.

‘If he can find the money, then that is up to him, but if not, he will find that the King does not have unlimited patience,’ adds an insider.

Family friends say although the matter has been temporarily resolved, Andrew’s ‘obstinacy’ has ‘soured’ family relationships.

• Adapted from Charles III: New King. New Court. The Inside Story by Robert Hardman, to be published by Macmillan on November 7.