The Saturdays singer, who lost out to television presenter Caroline Flack in the most recent series of the show, announced she is to become a mother again later this year.
The couple’s first child, a son, Parker, was born in October 2013.
The pop star was a firm favourite with the public on Strictly, but has been forced to pull out of the show’s forthcoming UK tour due to illness.
A tour organiser said Frankie is currently suffering with severe sickness known as hyperemesis gravidarum, which has also affected the Duchess of Cambridge during her pregnancies.
The spokesman said: “We completely respect Frankie’s decision; a safe pregnancy is the priority. On behalf of the whole cast and crew, we send Frankie our love and very best wishes – we will miss her.”
In a statement issued through the tour, Frankie said: ” Wayne and I are delighted to announce that we are expecting our second baby. It is very early days, but we couldn’t be happier and Parker will make a wonderful big brother.
“Although this is such an incredible time for us as a family, due to health reasons I am sadly unable to go on the Strictly tour as planned.
“I’m devastated that I’m missing out, as I loved Strictly so much and was so looking forward to joining everyone again in all those fabulous arenas. Thanks for the warm messages I’ve already received, they are really appreciated.”
The producers will announce tomorrow the name of a new celebrity performing in the arena tour.
Frankie’s husband retired from football last year, having played for clubs including Chelsea, Manchester City and Southampton, and was also capped for England.