To become King of England in Bitlife, you must either be born as a son of the King of England or as a prince of the royal family. You can also marry into the royal family by dating a royal through the dating app under the in-game Love Activity tab.
However, being born royal and marrying into the family requires a bit of luck. The chances of this happening can be increased if you choose the UK as your place of birth.
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You can also try to reroll characters until you get one as a prince of the English royal family or a member of the royal family. If you're lucky, you'll have to wait until the current king dies to become King of England.
For the wedding option, you will have to keep finding dates until you find one who is a princess or a member of the royal family. If you manage to find a royal to marry, then you can attempt to become king by outliving all the other royals or murdering your way to the throne.
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