Before getting into the K-1 process I would always advise obtaining competent legal advice from a licensed American attorney. Thailand can be very difficult to start the process however thousands have completed the process without many problems.
Essentially a K3 visa was designed as a fast alternative to the immigrant visas (IR1/CR1). K3’s are a non-immigrant visa so one cannot stay indefinitely in the United States on one of these visas. For the Thai/American couple looking to immigrate to the USA, the K-3 is a good choice if time is of the essence.
Advance Parole gives a Thai fiancée the right to re-enter the United States on a K-1 Visa after leaving the country. This is important because your fiancée cannot leave the country on a K-1 Visa and return without obtaining this crucial travel document.
Not being an expert in Thai contract law I decided to look at what effect is given to prenuptial agreements in Thailand. I found that generally speaking, so long as the Prenuptial agreement is registered at the time of the marriage the courts in Thailand will uphold the agreement.
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When a US Citizen sponsors a Thai fiancé/fiancée or spouse for immigration to the United States the US Citizen must show that he/she can support the Thai immigrant. The US government is interested in making sure that an immigrant brought to the US (for our purposes a Thai loved one) will not become a public charge (welfare recipient).