Sienna Miller’s secret dinner at King’s hideaway as she weighs up key royal charity role… Hope she changed out of her amazing outfit from the night before!

Sienna Miller has had a secret dinner with the King and a VIP tour of Dumfries House in Scotland.

The Hollywood actress joined Cabinet Ministers including Chancellor Jeremy Hunt and members of the Privy Council to help the King celebrate 15 years of the restoration of the Ayrshire mansion he saved for the nation.

Ms Miller, 41, who revealed her pregnancy bump in an eye-catching outfit at the Vogue World party last week, was invited to stay over in the historic £45 million house.

It is not known if the actress’s boyfriend Oli Green, 26, was invited. The actor will appear in the sixth season of The Crown when he plays law student Rupert Finch – a former boyfriend of the Princess of Wales and Prince William’s love rival at St Andrews University.

An insider said that Ms Miller was one of a handful of celebrities considering becoming an ambassador of the King’s charitable Foundation which has its headquarters at Dumfries House.

Her visit on Friday was designed to help her decide whether she would accept.

The Hollywood actress joined Cabinet Ministers including Chancellor Jeremy Hunt and members of the Privy Council to help the King  (pictured) celebrate 15 years of the restoration of the Ayrshire mansion he saved for the nation

Earlier this year, the Layer Cake actress attended a celebrity-studded event for the Prince’s Trust, the King’s other long-running charity, alongside Rita Ora and Kate Moss.

But this would be the first time she has agreed to become an ambassador for the Prince’s Foundation, which gives young people the chance to develop skills with projects that range from the hospitality to textiles industries.

The Foundation, however, has come under fire in recent years. Michael Fawcett, the King’s long-time aide, was forced to step down from his role as the charity’s chief executive over a scandal involving millions of pounds of donations from foreign tycoons.

Two staff members were questioned by police after The Mail on Sunday revealed documents in which wealthy foreign tycoons appeared to have been offered help to get honours – including a knighthood – in exchange for donations.

An insider said that Ms Miller was one of a handful of celebrities considering becoming an ambassador of the King’s charitable Foundation which has its headquarters at Dumfries House

But the Metropolitan Police announced last month that they had concluded their investigation and would not bring any charges. An insider said there was a fresh drive to sign up celebrity ambassadors to rehabilitate the charity’s image.

The source said: ‘There is a new sense of optimism in the charity.

‘So on Friday there were some celebrities including Sienna Miller and lots of leading politicians there too. But a private dinner for something to celebrate a house that’s open to the public seems like a strange thing if you ask me.’

Before the dinner, the King held a reception to mark the 15th anniversary of the opening of Dumfries House and estate to the public.

At 5.30pm he hosted a meeting with the Privy Council attended by Penny Mordaunt, Jeremy Hunt and Grant Shapps.