The King has appointed the Duke of Edinburgh to the Order of the Thistle as four new images of him are released to mark his 60th birthday.

Appointments to the order – the highest honour in Scotland – are entirely in the personal gift of the King and do not require prime ministerial advice.

The three other new recipients of the order are anthropologist Professor Dame Sue Black, distinguished lawyer Baroness Helena Kennedy and Scotland’s first black professor Sir Geoff Palmer.

The new appointments are effective from Sunday, and the installation ceremony is expected to take place over the summer.

The order has a complement of 16 knights and ladies, and in addition the Queen, the Princess Royal and the Duke of Rothesay, as the Prince of Wales is known in Scotland, are Royal Knights of the Thistle.

READ MORE: King Charles seen in public for first time since cancer diagnosis

Charles made Edward the Duke of Edinburgh to mark his 59th birthday, and he had his first solo engagement with the title at the Palace of Holyroodhouse a few days later, hosting participants in the Duke of Edinburgh Awards.

Queen Elizabeth II granted him the additional title of Earl of Forfar to mark his 55th birthday, and he holds several patronages of Scottish charitable organisations including the Edinburgh International Festival.

Prof Black is an anatomist and forensic anthropologist whose research on human morphology and biometrics has been used to assist with international war-crime investigations and to identify those involved in mass-fatality events.

Baroness Kennedy is the recipient of 42 honorary degrees from many universities, including those of Glasgow and Edinburgh, in recognition of work on women and the law and on widening participation in higher education.

She has also been honoured by the governments of France and Italy for her considerable work on women’s rights.

Sir Geoff pioneered the use of the scanning electron microscope to study cereal grains using research from his PhD, sits on the boards of community organisations and has received honorary degrees from various academic institutions.

He has published books on race relations and cereal science and technology.

In newly released images, Edward is pictured wearing a red jumper underneath a dark buttoned waistcoat, and smiling with his three dogs, Labrador Teal, cocker spaniel Mole and Labrador puppy Teasel.

The King’s brother, the youngest child of Queen Elizabeth II, will celebrate on Sunday.

In a rare newspaper interview, Edward said the monarchy is “as important as ever” in “trying to bring people together”.

He told the Daily Mail: “Our role – being part of the monarchy – in trying to bring people together is as important as ever, if not more so today.

“I think we all wonder how we can reach out to those communities who perhaps don’t always think that this, the monarchy, is something for them.”

The duke carried out a series of engagements with the Duchess of Edinburgh earlier this week, ahead of his milestone birthday.

He was presented with a Leeds Rhinos rugby shirt with “HRH 60” on the back to mark the date, during a visit to Headingley Stadium in Leeds on Friday.

Edward noticed the detail on the back and said to his wife: “Yours is more subtle than mine.”

He told the young players: “Thanks a bunch. I really need to be reminded.”

Sophie then paid a tearful tribute to Edward at the end of the Community Sport and Recreation Awards, saying he was “the best of fathers, the most loving of husbands and he is still my best friend” and she was “so proud of the man he is”.

The slimmed-down working monarchy has been under increasing pressure, with some leading members of the royal family ruled out of public-facing duties.

Charles, 75, is undergoing treatment for cancer and the Princess of Wales is recuperating from abdominal surgery.