In Java: What happens if I change a key in an HashMap to be equal to another key?

I know that I can not have 2 keys in a HashMap which are equal (by the equals()-method). And if I try to add a key-value-pair to the HashMap with the key already existing, the old value is just replaced by the new one.

But what if I change an already existing key to be equal to another existing key?

How will the map.get() method behave in this case (applied to one of these equal keys)?

Very simple example below.

public class Person{
  private int age;
  private String name;

  public Person(int a, String n){
    age = a;
    name = n;
  }

  public void setAge(int a){ age = a; }
  public int getAge(){return age; }
  public String getName() {return name; }

  @Override
  public boolean equals(Object o){
     if(!(o instanceof Person)){return false;}
     Person p = (Person) o;
     return ((p.getName().equals(this.getName())) && (p.getAge() == this.getAge()));
  }

  @Override
  public int hashCode(){return age;}
}

public class MainClass{
 public static void main(String[]args){
   Person p1 = new Person("Bill", 20);
   Person p2 = new Person("Bill", 21); 
   HashMap<Person, String> map = new HashMap<>();
   map.put(p1, "some value");
   map.put(p2, "another value");
   p1.setAge(21);
   String x = map.get(p1); // <-- What will this be??
   System.out.println(x);  
 }

}