Complex sentence: The princely title had been used for sons of the sovereign since Tudor times and was formalised by Letters Patent of 30 November 1917, while the style of "Royal Highness" had been used since the Restoration and was confirmed by Letters Patent of 3 February 1864.
Split into simpler sentences: The princely title had been used for sons of the sovereign since Tudor times and was formalised by Letters Patent of 30 November 1917. The style of "Royal Highness" had been used since the Restoration and was confirmed by Letters Patent of 3 February 1864.