"It's impossible to keep a secret ... especially one as wonderful as this," they announced on their website. "We want to be the first to share this great news with everyone that we are expecting a new addition to our family. Love, John, Kelly and Ella."
Travolta, 56, and Preston, 47, lost their son Jett when he died of a seizure in 2009. They have a 10-year-old daughter named Ella Bleu.