The Chelsea midfielder joined Phillip Schofield and Holly Willoughby in the studio on Thursday for a chat, with the conversation soon turning to weddings.
Phillip cheekily asked Frank: "So when are you going to make an honest woman out of her?" - referring to the Dancing on Ice presenter.
"There have been so many rumours about weddings getting postponed and all this kind of nonsense - we never had any wedding planned but we are certainly going to get married," Frank replied.
"But we would love to do it when no one knows and we are just done - no big show. That will be our style I think."
The couple have been together since 2009 and announced their engagement in 2011.
There has been speculation that their wedding could take place at a venue in Christine's native County Down.
Meanwhile, in what may be seen as a surprise move by a footballer, Frank is also launching his new children's book which he says has been a dream of his for a number of years.
"I just wanted to look at something I could do in my own time," he explained.
"I came up with the idea for (the book) about four or five years ago and to be honest I didn't have the confidence to go ahead and actually do anything about it.
"I had the characters in my head, I had an idea of stories and then about a year or so ago I actually thought "right I'm going to try and do something" because I'm getting a bit older in football years.
"And that's when I actually took the bull by the horns and started writing out the stories and putting it down on paper."