The couple already have a three-year-old son named Winston.
Billie has previously said she would like to have another child although was in no hurry.
“I am one of four and I always thought I would have a big family. Who knows what will happen? It’s funny because when you get engaged, everyone asks when you are marrying.
“Then when you have a child, they ask when you are going to have a second one. We will just have to wait and see.”