Tim Mathieson, 66, will face a plea hearing in Melbourne Magistrates Court in October.
Mathieson, who faced court by videolink under the name Raymond Mathieson on Thursday, admits sucking on a woman's nipple without her consent in East Brunswick in March last year.
Two weeks later Ms Gillard told the Adelaide Advertiser the couple had split more than a year earlier.
She and Mathieson, a former hairdresser, were together for a decade and lived at the The Lodge and Kirribilli House throughout Ms Gillard's three-year term as prime minister.
Mathieson's lawyer Brad Penno had asked in a previous hearing for his client to be granted diversion out of the justice system, which would allow him to avoid a criminal conviction.
On Thursday Mr Penno said that had been taken off the table and asked for an adjournment for a pre-sentence hearing.
Mathieson will return to court on October 19.
1800 RESPECT (1800 737 732)
National Sexual Abuse and Redress Support Service 1800 211 028
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