Original: When the 15-year-old King lay dying in June 1553, he nominated Jane as successor to the Crown in his will, thus subverting the claims of his half-sisters Mary and Elizabeth under the Third Succession Act.
Simplified: When the 15-year-old King lay dying in June 1553, he nominated Jane as successor to the Crown in his will, thus subverting the claims of his half-sisters Mary and Elizabeth.