The 35-year-old professional tennis player - who is expecting her first child with fiance Alexis Ohanian - is currently gracing the cover of Vanity Fair magazine where she shows off her burgeoning baby bump, reported Contactmusic.
Ask her if she could put Serena on a scale from one to 10 based on her cover shoot, Christie says, "Gorgeous. She's an 11. She's off the scale. She is over-the-top amazing."
And the 63-year-old model - who has daughter Alexa, 31, from her marriage to musician Billy Joel, son Jack, 22, with third husband Richard Taubman, and daughter Sailor, 18, with her fourth husband Peter Cook - says the tennis champion is the epitome of success.