Conversation so far:
What celebrities has Oprah Winfrey interviewed?
In 1993, Oprah Winfrey hosted a rare prime-time interview with Michael Jackson.
Who else has Oprah Winfrey interviewed besides Michael Jackson?
On September 10, 2007, David Letterman made his first appearance on The Oprah Winfrey Show, as its season premiere was filmed in New York City.

Question: When did she appear on the late show?
Self-contained rewrite: When did Oprah Winfrey appear on the late show?