Complex sentence: Charles's great-uncle, the 81-year-old Emperor Franz Joseph attended and, relieved to see an heir make a suitable marriage, was in good spirits, even leading the toast at the wedding breakfast.
Split into simpler sentences: Charles's great-uncle, the 81-year-old Emperor Franz Joseph, attended the wedding. He was relieved to see an heir make a suitable marriage, and was in good spirits, even leading the toast at the wedding breakfast.