From Longman Dictionary of Contemporary Englishascend the throneascend the thronePGto become king or queen → ascend
Examples from the Corpus
ascend the throne• He acquired it partly by accident, for war was near when he ascended the throne.• Start there, with Caliban ascending the throne.• Primarily, however, her antics seem playful, befitting a king who ascended the throne at age 10.• The original sovereign continued to be struck until 1603, when James I ascended the throne, but was revived in 1817.• For a number of years after he ascended the throne he remained highly deferential to gentry concerns. 