Ashley Graham expecting twin sons: 'Are you serious?'

Sept. 20 (UPI) -- Ashley Graham is pregnant with twins.

The 33-year-old model is expecting twin sons with her husband, Justin Ervin.

Graham shared the news Monday on Instagram alongside a video that shows her and Ervin learning at an ultrasound that they are having twin boys.

"Are you serious?" Graham responds. "We're gonna have three boys!"

"You're kidding me!" Ervin says.

Graham showed off her baby bump in a slideshow of photos last week.

"sun's out, bumps out," she captioned the post.

Graham and Ervin married in 2010 and already have a 20-month-old son, Isaac Menelik. Graham announced in July that she was expecting another child with Ervin.

"the past year has been full of tiny surprises, big griefs, familiar beginnings and new stories. i'm just beginning to process and celebrate what this next chapter means for us," Graham said on Instagram.

Graham had nothing but praise for Ervin while celebrating Father's Day in June.

"happy father's day @mrjustinervin. isaac is so fortunate to have such a supportive, loving compassionate, and incredible dad like you," she said on Instagram. "getting to witness you be a father is the greatest gift."

Graham is known for her modeling work with Lane Bryant, Addition Elle and Sports Illustrated.