In a tweet he wrote "again another lie … spreading nonsense" about her.
The denial comes when McPartlin, 42, has moved into a fenced-in six-bedroom house in a quiet suburb of London, which is said to be leasing £ 12,000 a month.
The neutrally decorated property, spread over three floors, also has a games room, a bar and balconies overlooking large gardens.
The presenter lived in Chiswick, in the west of London, with Mrs. Armstrong, while her best friend, Declan Donnelly, lived in the same street.
McPartlin's apparent move came after he confirmed last Thursday that he would delay his return to television to focus on his recovery.
He has undergone rehabilitation since March for a two-year addiction to painkillers following an unsuccessful knee operation.
The delay led to the next ITV series of Ant and Dec & # 39; s Saturday Night Takeaway which was hired until 2020.
The star also delayed his return to I'm Celebrity … Get Me Out of Here! until 2019.
McPartlin said in a statement: "My recovery is going very well and to continue, after talking with Dec and ITV, I made the decision to stop the rest of the year.
"I would like to thank both the Dec and the ITV for their continued support and I can not wait to get back to work in the new year."
The presenter now comes out with his former personal assistant Anne-Marie Corbett.
A source revealed: "Anne-Marie put him back together, she was his rock."
ITV CEO Carolyn McCall said that he "wanted Ant very well" and added that he would have to spend all the time necessary to recover before returning to the channel.
"He will not be back for a moment too soon," he said.
"He will come back when he is well and when he is ready to return.
"ITV will not put him under any pressure to return unless he is well and fit enough to go back."
When he insisted that McPartlin would surely return to ITV, Mrs. McCall said that "as far as I know, it's true."