The 28-year-old singer's engagement to Bell ended with their split in 2011, but the news of the couple being back together surfaced last year, reported Contactmusic.
"Nadine is on cloud nine after Jason went down on one knee over Christmas and proposed. She is a traditionalist at heart and has told friends they will become a 'proper family' after they tie the knot," a source said.
"She hasn't started planning the wedding yet as obviously she is set to drop any second now. But she can't wait to organise a big white wedding once she's settled into motherhood," the source added.