It's not like the role requires a stretch--the former Sarah "Fergie" Ferguson plays herself. She runs into Joey (Matt LeBlanc) and Chandler (Matthew Perry) as they're tooling around London's Westminster Abbey.
Seems the entire cast, with the exception of pregnant Phoebe (Lisa Kudrow), is filming the season's final episode in England this week.
The storyline: All (almost) the Friends (Rachel, Monica, Ross, Joey and Chandler) have traveled abroad to attend a spur-of-the-moment wedding. Elliott Gould and Christina Pickles (Ross and Monica's parents, Jack and Judy Geller) also guest star.
The one-hour cliffhanger airs May 7.
"I am very pleased to be here," London's Evening Standard quotes the Duchess. "I was really excited about appearing on Friends and meeting the characters." And it's got to beat that Weight Watchers gig.
And what did the Friends think of Fergie? Says LeBlanc: "The Duchess is really, really nice."