Simplify the following text for a Grade 11 native English-speaking person.
Original: He acquired much favor with the Emperor Hadrian , who adopted him as his son and successor on 25 February 138 , after the death of his first adopted son Lucius Aelius , on the condition that Antoninus would in turn adopt Marcus Annius Verus , the son of his wife 's brother , and Lucius , son of Aelius Verus , who afterwards became the emperors Marcus Aurelius and Lucius Verus .
Simplified: The Emperor Hadrian adopted him as his son and successor on 25 February 138 , after the death of his first adopted son Lucius Aelius . The condition was that Antoninus would in turn adopt Marcus Annius Verus , the son of his wife 's brother , and Lucius , son of Aelius Verus , who afterwards became the emperors Marcus Aurelius and Lucius Verus .