Original: The Duke of Roxburghe is the Premier Baronet of Scotland by his Baronetcy of Innes-Ker of Innes created in 1625.
Simplified: The Duke of Roxburghe, who is also Baronet of Innes-Ker of Innes is the Premier Baronet of Scotland because the baronetcy is the oldest one still existing in Scotand. It was created in 1625.