Aaron Johnson, Sam Taylor-Wood Expecting Second Child

By Alison Schwartz

Friday July 29, 2011 05:00 PM EDT

Sam Taylor-Wood and Aaron Johnson

Fred Duval/FilmMagic

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Aaron Johnson is getting ready to pull double-daddy duty – his fiancée, filmmaker Sam Taylor-Wood, is expecting the couple's second child, her rep confirms to PEOPLE.

The Kick-Ass star, 21, and Taylor-Wood, 44, whose romance raised eyebrows because of their 23-year age difference, are already the proud parents of a baby girl, Wylda Rae, who just turned 1.

After stepping out together as a couple last spring, Johnson defended their relationship. "I've got a wonderful woman. I'm an old soul, and she's a young soul."

PHOTOS: Who's Due Next?

Taylor-Wood, who also has two daughters from her first marriage to art dealer Jay Jopling, met in 2009 on the set of her directorial debut, Nowhere Boy.

• Reporting by SIMON PERRY