Becoming A Brit

Not just anyone can become a Brit and although Meghan Markle has decided in order to become a Royal she has to become British she will still have to undergo the barrage of tests before she can ditch the American passport and pop a nice shiny British one into her purse instead.  
Marrying a Brit, even a Prince, will not mean an automatic UK passport so she will have to apply for a fiancee or spouse visa which means she will have to meet a range of suitability criteria, as well as vouching that her and Harry are the real deal, showing they intend to live permanently together in the UK and have a genuine relationship during a visit from immigration.
The betrothed must also meet a minimum income rule, which stipulates that a Briton must earn at least £18,600 a year - or have savings equivalent to £62,500 - to bring their partner to the UK.
Harry will also need to show he can support Meghan without recourse to public funds, and show evidence they have suitable accommodation that is not overcrowded or dangerous.
Ms Markle can then apply for citizenship after she has had three years of lawful residence in the UK as long as she pays the £7,000 in fees and processing.
That's not the end of the process though.
To have the status approved there are a few more hoops to jump through - not least the notorious life in the UK citizenship test, requiring the applicant to swot up on about 3,000 facts and 278 historical dates.
Then she can call herself a Brit but not a Princess as you have to be born into the Royal family to be one of those although whether she carries on being Meghan or uses her real name Rachel is her choice.