Frank and Lily Tennyson the parents of Gwen and Ken (Ben 10: Alien Force). They were discussed in "Goodbye and Good Riddance", but they haven't made an appeareance yet. Gwens father, Frank, recieves a new career during the end of the episode, causing them to move to Ben's home town. In Ben 10: Alien Force, it was revealed that they had a son named Ken. In "Max Out", Gwen told Kevin that she had a brother named Ken and Kevin joked about their parents' names being Sven and Jen since most of the Tennyson's names rhyme. Ben Tennyson says hello to his Uncle Frank.
Their first appearance in the Ben 10: Alien Force series was in, "What Are Little Girls Made Of?''.

Frank And Lily Tennyson's First Appearance
What Are Little Girls Made Of?

Frank And Lily Tennyson's Last Appearance
What Are Little Girls Made Of?

see also: Tennyson Family