The "secret menu" item was once a limited-time offer back in 2010 that garnered its fair share of fans and features a stack of buttermilk pancakes layered with cinnamon roll filling and cream cheese icing.
The reason you can now get it for a limited time is because the same cinnamon roll and cream cheese icing are being used for the chain's Cinnamon Roll French Toast (the April 9th date is likely when they're take the Cinnamon Roll French Toast off the menu), which also means you can probably convince your server to ring you up an order of Cinn-A-Stacks the next time they add something cinnamon roll-y to the menu.
Photo via IHOP.