"Lorde was beyond nervous, she said what got her through it was able to think about singing it it David, which was really beautiful," he told Periscope.
He also gave some insight into Bowie's belief that Lorde would pave the way for modern music.
"David really liked Lorde, and he sort of felt like she was the future of music, and they had a few wonderful moments together," Garson said.
"She was the perfect choice. I actually think some of David's family members and David's management had some suggestions that she would be the right one... They wanted to bring the next generation in."