star was "visibly flustered" when Penelope, who he dated for three years before they split in 2004, approached him at a pre-Oscars party in Beverly Hills on Friday night.
A source said: "Penelope tapped him on the shoulder and timidly asked,'Tom?'
"Tom turned around, got visibly flustered and awkwardly said, 'Oh, hey. Hi', and gave her a small, distant hug before turning back around to his friends. It was weird."
The 46-year-old actor is now married to actress Katie Holmes, who was absent from the party, hosted by the head of Creative Artists Agency Bryan Lourd. The source told the
New York Post
newspaper: "Katie was not there. But he clearly hasn't run into Penelope very often since they split."
Madonna, Sir Elton John, Oprah Winfrey, Tom Ford, Mike Myers, Shirley MacLaine, Meg Ryan, Tobey Maguire and Leonardo DiCaprio were also at the party.