A few months after she played John Lennon's iconic white piano, Lady Gaga joined his widow Yoko Ono onstage in Los Angeles at a concert prefacing a weekend of celebrations beginning October 9, to celebrate what would have been Lennon's 70th birthday.

Though pictures of Gaga at the piano drove fans into an outraged tizzy, causing son Sean Lennon to remove the offending picture from Twitter, the pop star's appearance at the end of the three hour concert by the Plastic Ono Band was less controversial. "Thanks for being so brilliant and such an inspiration to so many women," Gaga, 24, told Ono, 71, according to BBC News. Ono returned the favor, calling Gaga,"so brilliant and such an inspiration to so many women."

Celebrations planned for Lennon's 70th will culminate in Ono's lighting of the Imagine Peace Tower in Iceland, inscribed with the words, "I dedicate this light tower to John Lennon, my love for you is forever, Yoko Ono." Ono was also joined by RZA, members of Sonic Youth, as well as Vincent Gallo and others from the avant-garde art world. Gaga and Ono ended the concert by lying on top of the grand piano together. –AMY LEE

Watch video of the finale, "Give Peace A Chance" below: