During an interview with The Sun at the weekend, Ant praised his new girlfriend Anne-Marie Corbett for helping him recover from a drink-driving arrest and stint in rehab and appeared to criticise Lisa for her Twitter presence.
During Monday's Good Morning Britain, Piers said he imagines Lisa is "pretty hurt" by Ant's comments.
He said: "I think that there’s somebody else involved in all this, who is Lisa, who I know well, who I’d imagine is pretty hurt by it.
"I always find it funny when people say 'I've never been happier,' when they've already been married for 20 years, it’s a little bit like, would you say that?"
The star added: "I don’t think I would say something like that, because A, I don’t think it’s ever true.
"If you marry somebody you’re clearly incredibly happy at the time you get married aren’t you? It’s sort of slightly hurtful isn't it."
After being praised by one viewer for supporting Lisa, Piers wrote on Twitter: "Lisa is a lovely lady."
Lisa retweeted the message and replied with three kiss emojis.
I think that there’s somebody else involved in all this, who is Lisa, who I know well, who I’d imagine is pretty hurt by it.
In an interview published over the weekend, Ant - who entered rehab last year after pleading guilty to a drink-driving conviction following a car crash - claimed Anne-Marie had been his "rock" throughout his recovery process.
— Lisa Armstrong (@lisaAmakeup) 21 January 2019
He said: "Anne-Marie honestly is the fundamental reason for the great change in my life. She’s been my rock. She’s a beautiful soul. We’re very happy.
"I’m in the best place I’ve been in my life, to be honest with you. It’s great."
Ant also said he no longer speaks to Lisa, but noted they still share their dog Hurley "quite evenly", despite Lisa reportedly giving up custody of the pooch in order to move on from Ant.
He added: "I’ve not been on social media or put any of my personal views out there. It’s not my style. She can live her life how she wants to live her life and say what she wants but I prefer to keep that private."
Lisa and Ant split in January last year after 24 years together.
Leave us a comment on our Facebook page @EntertainmentDailyFix and let us know what you think of this story.