Cher is gonna be pissed! The beloved L.A. Zoo elephants she went to bat for — Billy and Tina — were secreted outta the zoo under the cover of darkness last night … TMZ has learned.

Sources connected to the L.A. Zoo tell us Billy and Tina were removed around 1:30 AM Tuesday and, presumably, loaded up to be shipped to Tulsa Zoo — a controversial move that prompted protests, a lawsuit and an angry letter to L.A. Mayor Karen Bass … which Cher and several other celebs signed.

We’re told the elephant exhibit at L.A. Zoo was empty Tuesday morning — no elephants, no keepers and the electric perimeter fence was off … clear indications the animals were on their way to Oklahoma.

Advocates for Billy and Tina have been all over the L.A. Zoo for years, because Billy and Tina, Asian elephants, have been kept in an enclosure far too small for them.

Zoo officials say they’ll have more room to roam in Tulsa, but as the letter to Mayor Bass said, “it is nearly impossible to humanely keep elephants in traditional zoos.”