Presumptive US Republican presidential candidate Mitt Romney is grandfather to new twin boys, his son Tagg has announced, tweeting that the babies were born through a surrogate mother.
"Happy 2 announce birth of twin boys David Mitt and William Ryder. Big thanks to our surrogate. Life is a miracle," Romney posted on Friday in a Twitter message accompanied by a photograph of him and one of the babies.
Romney explained in a Facebook message that the surrogate was "gestational", meaning the babies are the biological product of Romney and his wife Jen.
"Everyone is healthy and happy," he wrote.
"For those keeping score at home, these are grandchildren numbers 17 and 18 for my parents."
Tagg is the eldest of five children of the Republican White House candidate and his wife Ann Romney, who celebrated the births with her own tweet minutes after Tagg's announcement.
"Grandchildren 17 and 18 are here. Congratulations @TRomney and Jen!"
The births bring the total number of Tagg Romney's children to six. His brothers and their wives have a total of 12 children among them.
Mitt Romney regularly refers to his grandchildren on the campaign trail.