The British TV icon only mentions Lisa in passing once in the book to gloss over the fact they got divorced.
The decision comes despite Ant and Dec's new book Once Upon A Tyne lifting the lid on their almost three decade long careers.
While Dec, 44, opens up about his wife Ali Astall, Ant steers clear of his romances.
Ant writes: "...So much had happened to us both.
"I'd gone through rehab and a divorce and Dec had become a dad for the first time.
"These are seminal points in your life, huge moments that, especially in my case, could have gone either way."
Ant's decision to speak about Lisa mirror's that of the Strictly Come Dancing make-up artist who has also kept quiet about the breakdown of their relationship.
Despite intense media scrutiny and rumours, Lisa has kept a dignified silence – keen to keep a lid on their relationship.
In comparison, Dec is more than happy to go into detail about his big day with Ali.
Dec playfully revealed how Ant went above and beyond with his wedding gift.
Dec penned: "Prince Charles loves writing letters."
"When I got married in 2015, Ant got in touch with HRH.
"He politely declined the stag do (again, his loss) but he did send a handwritten letter to Ali and me, as well as a lovely wedding gift - a set of placements that were all watercolours he'd painted himself."
Daily Star Online has got to a representative of Ant McPartlin for comment.