The Hurt Locker star reveals his dad Lee recently celebrated the birth of a new son called Theo - although Renner is still adjusting to life as the eldest of now six siblings.
Revealing the family news on late night U.S. talk show Jimmy Kimmel Live! on Thursday (08Dec11), he said, "My dad's still making it happen. I'm 40 and I've got a six-month-old baby brother.
"I think he might have been disappointed that I haven't done anything (had kids yet) so you know...! His name's Theo. He (his father) goes, 'You've got a brother named Theo'. I was like, 'Awesome! Can't wait to see him'.
"I got to see him at my sister's wedding. He was hanging on my dad's little papoose or something, whatever he was wearing."