HM King Charles III has a love and respect for tartan. The King regularly can be seen in Scotland wearing his kilt collection, including Hunting Stewart, Balmoral and until recently the Rothesay tartan.
The Rothesay tartan technically belongs to the Duke of Rothesay which is a dynastic title of the heir apparent to the British throne (David Stewart, son of Robert III, became the first Duke of Rothesay in 1398 and was heir apparent to the throne of the Kingdom of Scotland). Between the Union of the Crowns in 1603 and Edward VIII’s time as heir apparent (1910 to 1936), the the style Duke of Rothesay was informally dropped out in favour of Prince of Wales, the premier British title for the eldest son.