Perhaps he was practicing for all those lullabies he's going to be singing, or maybe he's been hanging around Meghan Markle's patronage, the National Theater, for a bit too long.

Whatever the case, Prince Harry is known to crack a few dad jokes here and there. But for Commonwealth Day on Monday, the royal dad-to-be did so in song form as he and eight-months-pregnant Markle were leaving Canada House.

Before Commonwealth Day services at Westminster Abbey (and the duchess's outfit change), the Sussexes stopped by Canada House for a quick taffy-making demo with young Canadian children (whose country is very close to the duchess's heart, since she previously lived in Toronto). As the royal parents-to-be were departing the engagement, Prince Harry decided it was the perfect moment for some Sound of Music.

"So long, farewell..." the duke sang as they waved goodbye, before breaking into giggles. The whole room erupts in laughter along with him, and Markle doesn't even bat an eye (though we know with every bone in her former actress body she was itching to sing along). Oh, Harry, your dad jokes know no bounds. 

The video was captured by royal correspondent Lizzie Robinson, who said "Harry sings a few lines from the famous Sound of Music song ‘So Long, Farewell’ to a staircase lined with young Canadians as the couple depart Canada House."

This isn't the first time the duke has shown off his vocal range. On stage at London's Hamilton back in August, he sang a few notes of one of the songs performed by George III's character.

“You say…” he began, but laughed it off as the crowd burst into applause. “That’s definitely not going to happen,” Prince Harry said with a smile. “He did try, but I said ‘no,’” referring to the show's creator, Lin-Manuel Miranda.

And now, "adieu, adieu, to yieu and yieu and yieu..." because our coworkers can't put up with us humming this song for much longer.

RELATED: Meghan Markle Stepped Out for Commonwealth Day and Wait—Where's Her Engagement Ring?

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