"When I look at her... I find it so hard because it's quite personal actually," Goodrem, 33, says in the interview which will go to air on Sunday September 9.
The trailer teases a huge announcement coming from Olivia Newton John, who has been reciving treatment for her cancer diagnosis.
"The interview Olivia Newton-John knew she had to do," Sunday Night host Melissa Doyle says, adding that the the Grease star "wants to put the record straight while she can".
Goodrem and Newton-John have shared a close friendship for years, with the Born To Try singer playing her mentor in Channel 7's biopic Olivia Newton-John: Hopelessly Devoted To You which aired earlier this year.
The dramatic Sunday Night trailer ends with Melissa teasing, "Olivia's very personal announcement, in her own words."
Sunday Night airs September 9 at 8pm on Seven.