Actress Jennifer Garner who stars in the movie "The Odd Life of Timothy Green," which is now in theaters, says her husband Ben Affleck is "walking testosterone."

The actress stopped by The Late Show with David Letterman to promote the movie when they started to discuss Affleck turning 40 years old the following day.

"I don't know that he's as thrilled with the idea of 40 as I am," Garner told Letterman about her husband.

"What's the problem? Is it low T?" Letterman asked.

"Low T as in low testosterone? Are you asking about Ben Affleck's testosterone level? Really, David! He will thump you. Have you seen my husband lately? He is walking testosterone," replied the actress.

Garner's interview on Letterman took place```Tuesday.

Photo Gallery: Jennifer Garner and Ben Affleck Through the Years

Garner and Affleck welcomed their third child, a son named Samuel in February. The actress has openly admitted that Affleck wants a fourth baby but that she has not decided yet.

In her latest movie, Garner plays her first on-screen mother character as a wife who lost hope to have a child only to find a boy that appears in her life out of the blue.

She said the role was very similar to her real life situation and that she was very excited to play it.

Watch Garner on Letterman Below:

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Tags: Jennifer Garner Ben Affleck David Letterman