Tagg Romney with one of his new sons. (Photo: Twitter)

Mitt Romney is now a grandfather eighteen times over. Tagg Romney, the presidential candidate's eldest son, announced he and his wife are the proud parents of twin boys on Twitter today.

"Happy 2 announce birth of twin boys David Mitt and William Ryder. Big thanks to our surrogate. Life is a miracle," Tagg wrote along with a picture of him holding one of the infant boys. 

Tagg Romney, 42, is a managing partner at Solamere Capital, a private equity firm he founded after his father's failed 2008 presidential bid. Solamere is named for an area of the Deer Valley ski resort where the Romneys have a vacation home. According to his bio on the Solamere website, Tagg currently lives in Belmont, Massachusetts with his wife, Jennifer.