The Britain's Got Talent comedy duo and Strictly host will represent the BBC and ITV1 at the O2 Arena and have been secretly rehearsing together.
Forsyth, who won a 'Special Recognition Award' at last year's NTAs, will sing a cover of Nat King Cole's 'Let There Be Love'.
Ant & Dec, who famously scored hits with 'Let's Get Ready To Rhumble' and 'If I Give You My Number' under their Byker Grove alias PJ & Duncan in the '90s, will team up with Forsyth for part of the song.
The National Television Awards air tonight at 7.30pm on ITV1.
Ant & Dec could potentially win their 11th consecutive 'Entertainment Presenter' gong this evening, but face competition from Keith Lemon, Michael McIntyre and NTAs host Dermot O'Leary.
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