Kate and William use new Scottish titles as they join Charles and Camilla in Edinburgh

The Prince and Princess of Wales have joined King Charles and Queen Camilla in Scotland, where the King was presented with the honours of Scotland – the country's crown jewels – during a service of thanksgiving held at St Giles' Cathedral in Edinburgh.

Read more: Hour-by-hour guide to King Charles' Edinburgh celebrations - The Telegraph, 7-min read

Kate arrived wearing a favourite Catherine Walker blue coat dress, which she has previously worn at the Royal Family's Easter church service this year and at the Commonwealth Day service in 2022.

She accessorised with a pearl choker that once belonged to Queen Elizabeth II and was also worn by Princess Diana to a state banquet in the Netherlands. Kate previously wore the piece to the funerals of both Prince Philip and Elizabeth.

Kate and William's Scottish titles explained

While in Scotland, Kate and Prince William, both 41, aren't known as the Prince and Princess of Wales.

As per tradition, which states that senior married royals are also given regional titles, Kate and William were given Scottish titles on their wedding day.

Read more: What do British titles mean? - Yahoo Life UK, 3-min read

However, these titles were updated when Queen Elizabeth II died in September 2022. The couple are now known as the Duke and Duchess of Rothesay, which is the title reserved for the heir to the throne.

The Duke of Rothesay was historically the title held by the heir to the Scottish throne before the Union of the Crowns – when Scotland and England unified under a single monarchy – in the early 1600s.

While today's visit marks the first time Kate has used her new title, William was in Scotland last week launching Homeward, a five-year programme delivered by the Royal Foundation that will aim to demonstrate the possibility of ending homelessness.

What were Kate and William's previous Scottish titles?

Prior to the late Queen's passing, Prince William was given the title Earl of Strathearn upon his marriage to Kate, making her the Countess of Strathearn.

This is because Scotland has a different nobility system to that of England and Wales, and rather than being a duke, William was gifted the additional earldom by the Queen.

The nobility refers to the region of Strathearn in southern Perthshire, which was a sweet nod to the couple's meeting place of nearby St Andrews University.

Watch: King Charles' Scottish coronation marred by boos and chants of 'Not my King'

But it's not just Scotland where William and Kate's monikers are different; their titles change once again upon visiting Northern Ireland.

There, they are known as Baron and Lady Carrickfergus, another title they were gifted by the Queen on their wedding day.