In this case, the antenuptial contract (ANC) signed by Mocktail and Cocktail in Burundi was formally invalid ab initio because it did not comply with the legal rules of Burundi. However, Mocktail registered the contract in South Africa after a 5 months' delay.
In South Africa, the formal validity of an ANC is governed by the Matrimonial Property Act 88 of 1984. Section 7(1) of the Act sets out the requirements for a valid ANC, including that it must be signed by both parties in the presence of a notary public and two competent witnesses. It must also be registered in the Deeds Office within 3 months of the date of signature.
In this case, since the ANC was not signed in accordance with the legal requirements of Burundi, it would not be considered valid in South Africa. Therefore, the default matrimonial property regime of in-community of property would apply. This means that Cocktail would be entitled to half of the accumulated estate of Mocktail, instead of just a usufruct as stipulated in his Will.
Cocktail should consult with a qualified lawyer in South Africa to fully understand her rights and options in this situation.