Taking to Instagram on Monday, Lisa announced the happy news in a post alongside a snap of an ultrasound.
"Little ray of sunshine coming Earth side March 2022," she wrote.
The news was welcomed by a slew of fellow reality stars and celebrities, with singer Bonnie Anderson and fellow Bachelor alumni Tara Pavlovic and Florence Alexandra sending their well wishes.
"Omgggg that is going to be the cutest baby," Tara gushed, while Bonnie added, "Congratulations legends".
While the couple's forthcoming bundle of joy will mark the first child between the loved-up couple, Billy also has a seven-year-old son named Ollie from a previous relationship.