Julian Lennon had previously vowed never to perform his father John Lennon's iconic "Imagine".
But Lennon was so upset by the "unimaginable tragedy" of the Russian war on Ukraine that the singer first publicly performed his father's anthem of peace.
"As a human being, and as an artist, I feel compelled to respond in the most important way possible," Lennon wrote on Instagram Friday alongside a candle-light video performance of the song. "So today, for the first time, I publicly performed my dad's song, IMAGINE."
"But also because his songs reflect our collective desire for peace around the world. Because within this song, we are transported to a place where love and unity become our reality, if but for a moment." For..." Lennon wrote. "The song reflects the light at the end of the tunnel we've all been hoping for..."
The song, featuring Lennon sitting on a stool with a solo acoustic guitar accompaniment, was posted to Lennon's Instagram page on his 59th birthday. The demonstration was part of Global Citizen's social media rally, Stand Up for Ukraine, which is raising funds for the country in distress and refugees in the midst of Russia's brutal war.
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Lennon condemned Russia's "killer violence".
"Millions of innocent families have been forced to leave their homes and seek refuge elsewhere," Lennon wrote. "I am calling on world leaders and everyone who believes in the spirit of Imagine to stand up for refugees everywhere!"
In a separate Instagram post, Lennon wrote "Stand Up for Ukraine," writing, "Wonderful, well we can do that."
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Julian Lennon is the son of Beatles legend John and his first wife, Cynthia Lennon.
The couple married in August 1962, but separated six years later when Julian was five years old in November 1968. John Lennon married Yoko Ono in 1969. The couple had a son, Sean Ono Lennon, in 1975.
John Lennon was assassinated on 8 December 1980.