Complex sentence: Before his accession to the throne, Edward was the longest-serving heir apparent in British history, until surpassed by his great-great-grandson Charles, Prince of Wales, on 22 April 2011.
Split into simpler sentences: Before his accession to the throne, Edward was the longest-serving heir apparent in British history. He was surpassed by his great-great-grandson Charles, Prince of Wales, on 22 April 2011.