Britain's Prince Philip poses for photo with the queen to celebrate 99th birthday

Husband of Queen Elizabeth II is now by far the longest-serving consort of any British monarch

Queen Elizabeth II and the Duke of Edinburgh pose in the quadrangle of Windsor Castle ahead of his 99th birthday on Wednesday, on June 1, 2020 in Windsor, Berkshire. Press Association

Britain's Princess Elizabeth and Prince Philip wave to the crowds on their wedding day, from the balcony of Buckingham Palace in London. AP Photo

Britain's Prince Philip is greeted by some of the students of St Mary's College, in Cheltenham, England, as he left the playing fields of St Paul's College in 1957 AP Photo

Britain's Prince Philip pulls his mount up sharp during a polo match at Windsor, England, in 1965. AP Photo

Britain's Queen Elizabeth II sits next to Prince Philip in the House of Lords as she waits to read the Queen's Speech to MPs in London on May 9, 2012. AP Photo

Britain's Queen Elizabeth II, Prince Philip and their children, Prince Charles, right, Princess Anne and Prince Andrew, pose for a photo on the lawn of Balmoral Castle, in Scotland, in September 1960. AP Photo

Britain's Queen Elizabeth II and Prince Philip wave to people at Nassau's Clifford Park after their arrival in Nassau, Bahamas, in 1977. AP Photo

Britain's Prince Philip, in his role as Captain General of the Royal Marines, attends a parade on the forecourt of Buckingham Palace, in central London. AP

Britain's Queen Elizabeth II and her husband Prince Philip, Duke of Edinburgh arrive to attend Ladies Day at Royal Ascot race meeting, in Ascot, Britain, in June 2012 EPA

Prince Philip, the Duke of Edinburgh, waves as he is discharged from the King Edward VII hospital in central London, on June 9, 2012. EPA

Britain’s Prince Philip, the Duke of Edinburgh, posed with his wife, Queen Elizabeth II, at Windsor Castle on Tuesday, one day before he celebrates his 99th birthday.

The pair plan a quiet lunch at Windsor Castle, where they have been socially isolating because of the Covid-19 pandemic.

Prince Philip is now by far the longest-serving consort of any British monarch.

The rest of the royal family will send their best wishes to him on video calls.

"I haven't seen my father for a long time," Prince Charles, heir to the throne and the eldest of Prince Philip's four children, told Sky News last week.

"He's going to be 99 next week. Facetime is all very well. You really want to give people a hug."

The royals make little fuss about their birthdays in public but this year celebrations have been even more muted.

Traditionally, the prince's birthday would be celebrated with gun salutes in London.

But with social gatherings banned, the queen felt such royal ceremonies would be inappropriate and also cancelled tributes for her own birthday in April for the first time in her 68-year reign.

But Buckingham Palace did release a new photograph of the royal couple, taken last week inside Windsor Castle, to celebrate the prince's birthday.

Britain is still under coronavirus restrictions that limit the size of gatherings, and Prince Philip and the queen, 94, are well into the age most vulnerable to Covid-19.

Prince Philip married the future queen at Westminster Abbey in 1947 when she was 21 and he was 26.

Together they had four children – Charles, the Prince of Wales and heir to the throne, Anne, Andrew and Edward.

Prince Philip stepped down from royal duties in August 2017 after completing more than 22,000 solo engagements, but in recent years he has been rarely seen in public.

He broke retirement silence in April to issue a statement thanking those involved in the fight against the coronavirus pandemic.