The 39-year-old cyclist announced the birth of his second child with girlfriend Anna Hansen early Monday morning via Twitter.
"Olivia Marie Armstrong has arrived!" Armstrong tweeted.
Using Twitter to announce Olivia's birth should come as no surprise: Armstrong created an account for his then-unborn daughter back in April. "I'm 'bout ready to get outta here!" the newborn "tweeted" Monday.
The Tour de France champion has three other children with ex-wife Kristin Richard: Luke, 11, and twins Isabelle and Grace, 8. Armstrong and Hansen previously welcomed son Max in 2009.