Augmentio

 was ostensibly a prince from a far-off land on Tara, sent to win Princess Strella's hand after Reynart was missing, presumed dead. He was actually a Taran android working for Grendel of Gracht. His mission was to marry Strella, then murder her so that Grendel could rule.

Augmentio's identity was discovered by the Seventh Doctor, who turned him to Strella's side. Augmentio helped to free Titania from Grendel but was killed by Grendel. (PROSE: The Trials of Tara)