Liberal Leader Justin Trudeau announced the arrival of Hadrian, weighing in at 8 pounds and 3 ounces, on Twitter Friday morning.
"Welcome to the world, little Hadrian. 8lbs 3oz, Sophie is wonderful, Xavier and Ella-Grace couldn’t be prouder," he tweeted.
Hadrian is the third child for Trudeau and his wife, Sophie Gregoire.
He arrives hot on the heels of the Liberal policy convention in Montreal, where a very pregnant Gregoire appeared via Skype from the couple's home to address the audience in Trudeau's opening speech.
"I know you wanted to be here," Trudeau said to his wife from the stage. "Is there anything you want to tell people?"
"Well, for very obvious reasons," Gregoire responded, standing up in profile in front of the camera to show her pregnant belly, "I can't join you tonight physically, but it's an honour for me to be joining in like this."
The birth came on the 30th anniversary of the resignation of Trudeau's father, Pierre, as prime minister.
Members of Parliament from all parties are sending in their congratulations via Twitter.
Minister of Citizenship and Immigration Chris Alexander warmly congratulated the Trudeau family.
NDP MP Robert Chisholm also offered up a few words.
Deputy Liberal Leader Ralph Goodale coloured his congratulations with extra punctuation.