According to the News Of The World Christine negotiated the contract directly with the channel before sacking her long-term agent earlier this week.
And the paper reports that she will now join Adrian on the GMTV sofa in the autumn, in a deal thought to be worth around £6m.
The move could be a blow for the BBC, who were reportedly planning to make Christine a major part of their 2012 London Olympics coverage.
“This shows how ruthlessly ambitious Christine is,” a TV insider told the paper. “She went to ITV for the money but could have earned a fortune at the BBC in the next few years.
“If she had stayed, she would still have been very rich and she would have been the face of the Olympics.
Adrian – who quit The One Show earlier this year – is fronting ITV’s World Cup coverage which begins this week, before joining GMTV later in the year.
Christine is currently continuing to present The One Show alongside comedian Jason Manford, who was recently named as Adrian’s replacement, and Chris Evans, who co-presents the show on Fridays.