The list of documents required at Chiang Mai for a 1-year extension of stay base on Thai wife/children says, "In case of divorce must bring Divorce Certificate to show"
* Does that mean the legal proof of divorce previous to your current marriage? I mean, that's necessary in order to get a Thai marriage registration & certificate, which you need to include with the application anyway.
* Or is it for the case when you have divorced the mother of your half-Thai children?
TLDR : Answer Summary
To obtain a 1-year extension of stay in Chiang Mai based on being married to a Thai national or having half-Thai children, you must present a Divorce Certificate only if you are divorced from the mother of your half-Thai children. This requirement does not apply if you are still married to a Thai spouse; thus, the document serves to clarify the circumstances under which you are seeking the extension.