Complex sentence: Reginald McKenna, the Home Secretary, visited the colliery that day representing King George V, who was attending the marriage of Prince Arthur of Connaught and Princess Alexandra, 2nd Duchess of Fife.
Split into simpler sentences: Reginald McKenna, the Home Secretary, visited the colliery that day. He represented King George V, who was unable to visit because of his attendance at the marriage of Prince Arthur of Connaught to Princess Alexandra, 2nd Duchess of Fife.