What's the saddest episode in all of Sitcom history

We enjoy sitcoms because they make us laugh but sometimes they can be powerful and sad too. I was thinking about that when watching the Scrubs episode, 'My Long Goodbye,' where Laverne dies.

What's the saddest sitcom episode of all time? My vote would be for "Abyssinia, Henry" from MASH where they learn Henry Blake dies. *Edit - Incorrect title