He previously denied rumours linking him to American swimmer Allison Schmitt.
But the sports personalities, who were reportedly introduced by Michael Phelps, have reignited speculation they’re dating following a series of cosy Instagram snaps.
Allison’s Instagram snap on Sunday saw her enjoying a helicopter ride in Melbourne with Grant, 37.
Love in the fast lane? Swimming great Grant Hackett, 37, and Allison Schmitt, 27, reignited romance rumours, after allegedly being introduced by mutual friend Michael Phelps
The 27-year-old, dressed casually in a black knit sweater, beamed for the photo, alongside Grant who sported a white polo shirt and designer sunglasses.
Allison captioned the moment: ‘Took a flight to see quite the beautiful Melbourne sights,’ alongside the hashtags #adventure and #poet.
Daily Mail Australia has reached out to both Grant and Allison for comment.
Looking cosy: An Instagram snap shared by Allison on Sunday, saw the pair enjoying a helicopter ride in Melbourne
Back in May, Grant denied they were dating, telling The Daily Telegraph: ‘Allison has been a good friend of mine for years through swimming. There is nothing else further there.’
Speculation followed an interview in Woman’s Day magazine, where Allison revealed that the sportsman had a ‘special place in her heart.’
The brunette told the publication: ‘I have loads of respect for him. I know he has a great future ahead.’
Grant made headlines in April 2016, when he was questioned by police after allegedly groping a man’s nipple on a flight.
Denial: Back in May, the swimming champ denied they were dating, telling The Daily Telegraph: ‘Allison has been a good friend of mine for years through swimming. There is nothing else further there’
In February he was arrested after a fistfight with his brother Craig at his parents’ home on the Gold Coast, but was released without charge.
He was said to be ‘going off’ and ‘stabbing a chopping board’ before disappearing for several days.
Grant posted a photo of himself on Instagram a day after his arrest, sporting a black eye and bloody face and saying his brother had ‘beat the s**t out of me.’
Stateside: It’s been alleged that Grant was introduced to Allison by swim star Michael Phelps (pictured), during his 30-day stint in rehab in the US, to treat his alcohol and sleeping pill dependency, along with his mental health issues
Craig at the time said he had little choice but to throw the punch after a drunk Grant ran at him during an intervention by his family.
The next month he admitted he needed help, and fled the country to a 30-day stint in rehab to treat his alcohol and sleeping pill dependency and mental health issues.
He then spent a few months living with Michael Phelps, training together, and allegedly being introduced to Allison.
Family: Grant shares two children, twins Jagger and Charlize, seven, with ex-wife Candice Alley
The sporting icon returned to Australia in August, and is currently embroiled in a custody battle.
Grant shares two children, twins Jagger and Charlize, seven, with ex-wife Candice Alley.
The couple split in 2012 after five years of marriage.
Calling time: The couple split in 2012 after five years of marriage