In the TV spot, which debuted Thursday, viewers don't get to see the Olympic gold medalist's face, as he is shot only from behind. Details of the interview and what subjects were covered have also been kept under wraps.
"By not showing Bruce's face in the promo, ABC News is really just adding to the mystery and all of the questions that viewers have," Variety TV reporter Elizabeth Wagmeister said.
Sources tell ET that those involved do not want any information to leak prior to the interview out of respect for Bruce, but the secrecy may have other benefits as well.
"It's not going to hurt the ratings," Wagmeister said. "And I think that no matter what the promo does, viewers will be tuning in and this will be a ratings gold mine for ABC News. I think that Good Morning America, The View and all of ABC's digital properties are also going to capitalize off of this. It's going to be talked about everywhere."
Speculation that Jenner, 65, has reportedly begun a gender transition has been covered widely in the media, and the biggest question about Sawyer's interview is whether or not that will be the main topic of discussion.
The two-hour 20/20 special will air on April 24 at 9 p.m. PT/ET. According to the ABC release, the sit-down will be "far-ranging" and "exclusive."