After Morgan quit, Reid addressed the news on Good Morning Britain in a slightly frosty speech that ended: "It is certainly going to be very different, but shows go on and so on we go."
Writing a diary of the events for the Mail on Sunday where he described Reid as his "TV wife", Morgan commented: "Jeez, even my real ex-wife talks more fondly about me than that (and, in fact, did so overnight in a very supportive message)."
He said that many friends got in touch after seeing it to ask whether the pair had fallen out, but explained that he could understand why she reacted in that way.
Morgan wrote: "I suspect Susanna's feeling angry and sad at me leaving just when the show's soared to new audience heights, concerned for her own future, fearful of troll abuse for publicly backing me (she's had a repulsive barrel-load of that over the years just for sitting next to me), and general discombobulation at the dramatic turn of events."
Reid had mentioned their many disagreements in her speech and acknowledged: "He is without doubt an outspoken, challenging, opinionated, disruptive broadcaster. He has many critics, and he has many fans."
She also added: "Piers has decided to leave the programme. Some of you may cheer and others will boo."
However, Morgan said he hoped they would stay friends after their five years on air together, and confirmed that Reid had since apologised for her goodbye speech.
Revealing that she had called for a "clear-the-air chat", he wrote: "She apologised for the tone of her chilly goodbye, which was for all the reasons I suspected, and I apologised for leaving her in the lurch so suddenly."
He said that they had agreed to meet up for lunch when coronavirus restrictions allow and that they had left things on good terms.
Watch: Piers Morgan clears GMB dressing room and leaves Susanna Reid cut-out behind