There is no king of England. It's not a separate country that can have a king of its own.
If you mean king of the UK, next in line is Charles, the Prince of Wales. That assumes he outlasts his mother. Failing that, the next few in the line of succession as laid down by law are as follows:
2. Prince William, Duke of Cambridge
3. Prince George
4. Princess Charlotte
5. Prince Louis
6. Prince Harry, Duke of Sussex
7. Prince Andrew, Duke of York
8. Princess Beatrice
9. Princess Eugenie
10. Prince Edward, Earl of Wessex
and so we go on with further relatives.
Of course 3, 4 and 5 are all small children. In the sad event that both Princes Charles and William die while Prince George is still under 18, he will be king, but Prince Harry will be appointed Prince Regent to do the duties until Prince George is old enough.