For the first time, Julian Lennon sings his father's song "Imagine." Julian vowed never to sing it in public, unless "it's the end of the world." But, with the crisis unfolding in Ukraine, he sang the song for Global Citizen's "Stand Up for Ukraine." Learn more about how you can help donate food, water, shelter and medical aid for the millions of people displaced by the crisis in Ukraine with "Stand Up for Ukraine."