Minogue and Donovan also starred in the Australian soap Neighbours

But the stars, who hit number one with the duet Especially For You in 1988, will not perform together.

Minogue will sing with finalist Leon Jackson, who is being mentored by her sister, Danni. Donovan is to perform with Simon Cowell's Same Difference.

Meanwhile, opera singer Katherine Jenkins will duet with the bookmaker's favourite, Rhydian Roberts.

Hopefuls

Ladbrokes are offering 1/3 odds for Roberts to win, Jackson is 7/2 and Same Difference are 6/1.

An ITV spokesperson said the songs each performer will sing will be confirmed later in the week.

The fourth series of the show began in August with thousands of hopefuls auditioning.

Dermot O'Leary was introduced as the new host, while Danni Minogue joined judges Cowell, Sharon Osbourne and Louis Walsh.

The X Factor final will be broadcast live at 1915 GMT on Saturday, and the results will be unveiled in a later show at 2135 GMT.

The prize is a �1m recording contract.

Last year's winner, Leona Lewis, is currently at number one in the UK singles charts with Bleeding Love.