ET has obtained footage of Arnold Schwarzenegger’s alleged mistress Mildred "Patty" Baena singing onstage as she impersonates Marilyn Monroe's iconic version of "Happy Birthday, Mr. President." The footage — in which Baena smiles and laughs in between singing to the audience assembled for a party -- was taken the same day as Arnold, Maria Shriver and their children attended a quinceanera celebration for Baena's niece several years ago. Baena's performance onstage occurred at a different location than the church where earlier the Schwarzeneggers greeted the niece. At the church, the families seemed comfortable as they enjoyed the celebration together, long before Arnold's shocking separation from Shriver and his confession that he'd fathered a child out of wedlock.  (ETonline.com)