Heidi Scarlioni

Countess Scarlioni was the wife of Count Carlos Scarlioni, whom, unbeknownst to her, was in fact a Jagaroth.

Biography
The Countess assisted him in making preparations to steal the Mona Lisa, even going to the Louvre wearing a micromeson scanner to test it defences. However, while carrying this out, the scanner was stolen by the Fourth Doctor, an act she promptly reported to her husband, resulting in the arrest of both the Doctor and Romana.

Shortly after, the Countess was killed by her husband shortly after he revealed his true, alien origin to her. (DW: City of Death)