Just when you thought it was safe for Ron Swanson to go back in the water. However temporary a guest appearance it might have been, 'Parks and Recreation' fans were excited and full of "aww" to see Ron Swanson (Nick Offerman) potentially developing a non-Tammy love interest in Lucy Lawless' Diane. Unfortunately, the terrible wrath of Tammy 2 may rear its ugly head once more! And by ugly head, we mean the lovely Megan Mullally's return!

While we never truly believed that Lucy Lawless would stick around 'Parks and Recreation' season 5 beyond a few episodes, shippers may be disheartened to learn that their fledgling relationship is about to face its biggest challenge ever. TVGuide reports that Megan Mullally is due to return to the series beginning with the ninth episode "Ron and Diane," no doubt causing even more trouble for her ex-husband's happiness.

"Ron and Diane" comes as 'Parks and Recreation's' annual tradition of devoting an episode to Ron's relationships, usually titled some derivation of "Ron and Tammy." Of course, there's always the chance that Lucy Lawless' Diane could finally be the one to break the tradition, but being that Mullally is married to Offerman in real life, we don't see her going away anytime soon.

Apart from Mullally and a returning Kathryn Hahn, ‘Parks and Recreation’ season 5 includes guest appearances from  ‘Breaking Bad's' Jonathan Banks and Glenn Headly as Ben’s parents, while  current ‘House of Lies’ lead Ben Schwartz will reprise his role as hipster “Jean-Ralphio” for at least one episode.

What say you? Will Megan Mullally's Tammy II destroy Ron's happiness yet again? Will Diane fight back? Place your bets for 'Parks and Recreation' season 5 in the comments below!