Complex sentence: He was the paternal grandfather of Diana Spencer, who was just under 14 years old at the time of his death and would go on to marry Charles, Prince of Wales, heir to the British throne, six years later.
Split into simpler sentences: He was the paternal grandfather of Diana Spencer, who was just under 14 years old at the time of his death. Diana would go on to marry Charles, Prince of Wales, heir to the British throne, six years later.