The two had been stage partners for 45 years when a 380-pound Bengal tiger named Montecore sank its teeth into Horn's neck during a live performance and dragged him offstage in front of a stunned audience.
Horn, now 64, was partially paralyzed, suffering a damaged neck artery and crushed windpipe in the October 2003 attack.
The long-running "Siegfried and Roy" show immediately went dark.
Promoters wouldn't say if the duo's big cats would be involved in the single illusion planned for Saturday night. The act was expected to last no more than 15 minutes.
"I'm sworn to secrecy," said Maureen Peckman of the Keep Memory Alive Foundation, the event's host.
The performance at the Bellagio hotel-casino was to benefit the Cleveland Clinic Lou Ruvo Center for Brain Health. The center, which will treat brain disorders like those Horn now suffers, is set to open later this year in a building designed by architect Frank Gehry.
Siegfried and Roy's performance will air March 6 in a one-hour special on ABC's "20/20."
During Horn's long rehabilitation, both men have remained devoted to their exotic habitat on the Las Vegas Strip. The Secret Garden and Dolphin Habitat at The Mirage hotel-casino houses lions, tigers and leopards. Fischbacher, 69, has called it Horn's "reason to get up in the morning."
The pair have said they believe that Montecore sensed Horn was having a mini-stroke and was dragging him to safety, rather than attacking him. Animal experts have disputed that theory.
After a two-year review, federal investigators never determined what set off the tiger.
The U.S. Department of Agriculture did find that the "Siegfried & Roy" show failed to protect the audience because it had no barrier separating the exotic animals from the crowd.
The illusionists' production company, S&R Productions, received a letter of noncompliance but was not fined.
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