In lieu of her appearance, Holmes released the following statement to Us Weekly:
"I regret having upset Leah in the past and wish her only the best in the future."
The statement arrived after ABC News' Dan Harris announced on Friday's "Good Morning America" that Holmes - who was married to Scientology's most famous member Tom Cruise - would be making an appearance and disclose "what she is now saying about Leah."
In the "20/20" interview that has been previewed, Remini says that any criticism of Cruise was as if one were criticizing the Church.
She also explained how she was punished for saying something to Cruise and Holmes during a social visit when Cruise was "forcibly kissing" Holmes, according to Remini. It's unclear if Holmes' statement is referring to that incident.
Holmes, 36, was married to Cruise from 2006 to 2012. They have a nine-year-old daughter together named Suri. Holmes has been very tightlipped about Scientology since leaving Cruise. But the "Mission Impossible" actor did confirm in a court deposition that Holmes left the marriage to protect Suri from Scientology.
Remini's "20/20" special airs Friday at 10 p.m on ABC.