The 27-year-old star said the Black Sabbath frontman will not be performing at Jack's marriage to fiancee Lisa Stelly - who is due to give birth to his baby in April - because his rock style will be too heavy for the occasion.
When asked by E! whether the 63-year-old singer would be performing at the nuptials, she replied: "No. I don't really think rock music is quite appropriate for a wedding."
'The Fashion Police' host admits Jack has been joking with her because she is more emotional than him about his forthcoming child and marriage.
She added: "He makes fun of me because every time I'm around him I get teary eyed now.
"He's like, 'Stop it! Go Away. Stop being dramatic. Get out of my face.' Because I'm like, 'I'm so proud of you. You're moving into a new house. You're getting married. You're having a baby. You have the most amazing fiancÃ©e ever!' "