The Cooks Hill lad, who is down to the final seven contestants on the show, has worked with music greats such as Suzi Quatro and Harry Connick jnr during this season.

But it was Minnelli who really got Johnston shaking in his trademark skinny black jeans.

"Being mentored by Liza was one of the most intense things I've ever done," 18-year-old Johnston said.

"She has these massive eyes and she stares really intently at you.

"I found it a bit intimidating. But she gave me some great advice.

"She sees music from a different angle and that's a new experience for me."

The theme for tomorrow's Australian Idol, featuring Minnelli, is a stage and screen night.

It was a new genre for Johnston, who has been singing since he was four and cut his teeth in Star Struck.

"I've never really experienced musical theatre before, so to have someone from that background giving me constructive criticism was great," Johnston said.

Born in Wingham, Johnston has entertained Star Struck audiences since 2002, performing in front of more than 100,000 people.

Cabaret queen Minnelli has been performing in Sydney and is taking part in her first Australian tour in 20 years.

Minnelli is the daughter of two Hollywood legends, Judy Garland and director Vincente Minnelli.