Simplify the following text for a Grade 10 native English-speaking person.
Original: William , however , would be King even after his wife 's death , and `` the sole and full exercise of the regal power ( would be ) executed by the said Prince of Orange in the names of the said Prince and Princess during their joint lives . ''
Simplified: But it was added that `` the sole and full exercise of the regal ( royal ) power be only in and executed by the said Prince of Orange in the names of the said Prince and Princess during their joint lives . ''