In the words of Zac Efron, 'Where's Taylor Swift when you need her?' Despite learning to play the guitar the night before, Efron sang Happy Birthday to Ellen.
Zac could have called on Taylor to help. They've teamed up for a duet before on Ellen and were rumored to have dated.
Zac was on Ellen to promote his new movie 'That Awkward Moment.'
NEXT: Zac Efron Meets His Biggest Fan
Zac Efron Fan