However, he did pay a very warm tribute to his daytime TV pal, which apparently moved both Ruth and the birthday boy.
Calling Eamonn "the genuine king of breakfast television" on GMB this week, Piers' fellow host Susanna Reid joked: "You say that through gritted teeth."
Piers, however, insisted his compliment was sincere.
I'm just a prince in his wake.
"I think Eamonn is the king of breakfast television," he repeated. "Fifteen years, he did."
Following an interjection from showbiz correspondent Richard Arnold, Piers modestly suggested Eamonn was even more distinguished at the job than him - while still claiming to be TV royalty himself.
Piers continued: "He was the king. And I'm just a prince in his wake.
"But he is brilliant."
Sharing the clip with her 739,000 Instagram followers, Ruth thanked Piers in the caption: "Sorry you couldn’t make it to his party @piersmorgan but this message more than made up for it.
"@eamonnholmes was genuinely touched x #breakfast #legends."
Piers replied in the comments section: "I meant every word - your man is a legend.
"So sorry I couldn’t be at the party."
An overwhelmed Eamonn thanked well-wishers earlier this week on Twitter: "Goodness me... I really wanted to ignore this birthday but I'm a bit overwhelmed by those of you who have marked it for me with your gifts, your good wishes and kind remarks.
"In a world of so much hate and anger, thank you for your love and decency."
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