What is 'C.1.2', the new COVID-19 variant detected in South Africa?

A new 'C.1.2' coronavirus variant has been detected in South Africa and its mutations are associated with "increased transmissibility", according to a non-peer-reviewed paper published about the variant. It shares a few common mutations with the Beta and Delta variants, but also has a number of additional mutations. Scientists suspect it might be able to partially evade the immune response.