When the 24-year-old "closed my eyes and went for it" to win the mass sprint in Turin the Briton, one of the world's most famous bike racers, was nowhere near the closing action.
But the modest winner was swift to send wishes to the older man.
"I've known him for a long time," Girmay said.
"We raced a lot together in Belgium and I saw him here he said to me 'Hey kid don't beat your father, I'm almost old enough to be your dad you know'."
Girmay described himself as the "first Black African to win at the Tour", and dedicated the win to the whole continent.
Cavendish appeared delighted for Girmay.
"That's massive, for him, for the Tour, for Africa," said the often prickly sprinter.
"He's a legend now isn't he," the 39-year-old added.
Fortunately for Africa, Eritrea and Girmay the stage not only started early on Monday, but finished faster than expected.
Half an hour later torrential rain fell on Turin with lightning blasting through the skies.
Cavendish has been level on 34 Tour de France stage wins with all-time great Eddy Merckx since the Manxman's last victory when he sped over the line arms aloft at Carcassonne in 2021.
It was his fourth win on that edition racing for Quick Step after years in the wilderness suffering from Epstein Barr virus.
