The King will be wished happy birthday by the Duke of Sussex on the day he turns 75, it has been reported.

Charles will be spending his birthday attending two royal events but at some point during the day his son Harry is expected to phone his father, according to an online BBC report.

The King and his son have a strained relationship since Harry stepped down as a working royal and moved with wife Meghan and their family to America three years ago, for personal and financial freedom.

In a series of interviews since Harry left the monarchy the Sussexes have made a number of damaging accusations against the royal family.

Earlier this year, the Duke and Duchess of Sussex were asked to “vacate” their UK home just weeks after Harry’s damning book Spare was released.

Reports at the time claimed the move was sanctioned by the King and the decision removed their remaining foothold in the UK and further weakened ties with the royal family.

The King’s 75th birthday will be a working day for the monarch marked by gun salutes across the capital.

Charles will officially launch the Coronation Food Project with Camilla which aims to bridge the gap between food waste and food need.

The head of state and his wife will visit a surplus food distribution centre outside London and meet staff and volunteers to hear about the ways food waste can be used for social good.

Charles will also host a Buckingham Palace reception highlighting the work of nurses and midwives over the decades as part of the NHS 75 celebrations.

Among the guests will be around 400 nurses and midwives alongside the Chief Nursing Officer of England, Dame Ruth May, and Amanda Pritchard, the chief executive of NHS England.

Birthday celebrations began early for the King when on Monday he was guest of honour at a party staged in the grounds of his Highgrove home in Gloucestershire.

Charles joined a host of people, from community stalwarts nominated by friends and family who are also turning 75 this year, to representatives from organisations marking the same milestone, from the NHS to members of the Windrush generation.

Among the famous faces at the event were celebrity chef Raymond Blanc, The Repair Shop host Jay Blades and singer Leee John from the 1980s group Imagination.

Charles Philip Arthur George was born on November 14 1948 at Buckingham Palace.

After his birth – the first at the royal residence since 1886 – his father the late Duke of Edinburgh drove to Caxton Hall to register the event.

The King is likely to celebrate his milestone birthday privately with his family and friends.

At noon the King’s Troop Royal Horse Artillery, named by the King’s grandfather King George VI, will fire a 41-gun salute from London’s Green Park.

Then an hour later the Honourable Artillery Company will fire a 62-gun salute at Tower Wharf, Tower of London – an extra 21 for the City of London.