The delighted couple, who have been married for four years and have a two-year-old daughter, Amelie, said in a joint statement, "We're so happy to find out that we are pregnant again and can't wait to meet our new little member of the family early next year.
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"Needless to say, we're all super excited, especially Amelie who is looking forward to meeting her younger brother or sister."
Former S Club 7 singer Rachel, 35, shared her pregnancy news on her website, alongside a sweet picture of the family's shoes with their birth years chalked underneath. Next to Amelie's pink trainers were a pair of white baby shoes with the year 2014 written in chalk below them.
Rachel competed on Strictly Come Dancing in 2008, coming second to actor Tom Chambers in the final. She married husband Alex the following year and their daughter was born in November 2010.
The first-time mum said that she suffered from morning sickness for the first five months but still loved being pregnant. "I would love to have more," she said after her daughter's birth. "I don't know about lots and lots! I think two is lovely but you never know…"