The 'Mean Girls' star - whose post-rehab attempts to get her career back on track are being recorded in documentary series 'Lindsay' on Winfrey’s OWN network - initially planned to prank call her mentor, but Letterman quickly blew his own cover and had a serious chat about his famous guest instead.
Lohan asked the audience: "I think maybe I should just call her right now. Should we call Oprah?
"I think so. Do you have a phone? Have we got a phone?"
Retiring talk show host Letterman, 66, took the phone and in a feminine voice said: "Yes, can I speak to Oprah Winfrey please? Hi, this is, uh, Lindsay Lohan's secretary."
He quickly owned up to his real identity when Winfrey asked who was on the line, causing her to reply: "Very good, Dave! The David Letterman who's retiring?!"
