Billie Piper christened David Tennant "David Ten-Inch" after hearing the intimate details of his manhood from a friend.
They just take everything down in the house with me on when their mates come round. They just ignore that we are related. I don't blame them.
The 26-year-old actress - who appeared alongside David in BBC sci-fi drama 'Doctor Who' - was delighted when her friend told her about a night of passion she shared with David, as it gave her ammunition to tease him.
She said: "One of my friends who was privy to the information handed it to me on a plate!"
Billie also revealed while her mother is a huge fan of her raunchy ITV2 drama 'Secret Diary of a Call Girl' - in which she plays high-class prostitute Belle de Jour - her father is less keen.
She said: "They are OK with it, nothing really shocks them when it comes to certain choices I make. My dad doesn't watch it - that would be a bit weird. But my mum finds it hilarious!"
However, Billie's siblings, brother Charlie and sisters Harley and Ellie, are less supportive of her career.
The star revealed: "My siblings ignore anything I do. They find it embarrassing and I get that. They don't want my success to become the topic of conversation.
"They just take everything down in the house with me on when their mates come round. They just ignore that we are related. I don't blame them."