It has been reported a deal was only reached over this weekend and she could rake in as much as £1.5million.
Following that, Simon, 54, posted to approximately 9.5 million followers: "It's official. Cheryl is back. Be careful what you wish for!
"Most importantly she is a brilliant judge of talent."
Cheryl found herself out of the TV talent show altogether in 2011 when she took the opportunity to jump ship and join Simon on the American version of the programme, and was replaced by NDubz star Tulisa Contostavlos.
However, she was soon given the axe in favour of Nicole Scherzinger – who was co-hosting at the time with Mario Lopez - when it was thought US audiences would not be able to understand her Newcastle accent.
Cheryl has said she is looking forward to getting back on the show after a three year absence
A very open spat ensued between Cheryl and Simon, but the star recently forgave the new father and has begun to communicate kindly with him on social networking websites in the last year or so.
It is thought Simon had been trying to get her back on the ITV primetime show for a long time ever since ratings began to drop.
The lineup has dramatically transformed, with Nicole even taking a seat on the panel of Britain's version, but nothing seems to have pulled in viewers like when Chery was around.
The judge's table has seen Louis Walsh remain, while former Destiny's Child singer Kelly Rowland has come and gone, Dannii Minogue moved on, Gary Barlow has filled in for Simon and Sharon Osbourne returned for a brief stint in series 10.
Meanwhile, Simon worked with the likes of Paula Abdul, Britney Spears, L.A Reid and Demi Lovato in Los Angeles but the show failed to take off like it did in Britain.