In a suit to recover under an insurance or health maintenance organization contract, the insurer or health maintenance organization has the burden of proof as to any avoidance or affirmative defense that the Texas Rules of Civil Procedure require to be affirmatively pleaded. Language of exclusion in the contract or an exception to coverage claimed by the insurer or health maintenance organization constitutes an avoidance or an affirmative defense.
Tex. Ins. Code § 554.002