Who did Dave Grohl have an affair with? Aussie fans have a new theory.

Speculation is reaching fever pitch after Foo Fighters frontman Dave Grohl announced that he had welcomed a lovechild.

Grohl fathered the newborn, a baby girl, with an unknown woman, outside of his 21-year marriage to wife Jordyn Blum.

It is his fourth daughter, who he has welcomed alongside his daughters with Jordyn, Violet, 18, Harper, 15, and Ophelia, 10.

"I've recently become the father of a new baby daughter, born outside of my marriage," he wrote on Instagram.

"I plan to be a loving and supportive parent to her. I love my wife and my children, and I am doing everything I can to regain their trust and earn their forgiveness."

Despite the candidness of the post, fans didn't miss that he had not disclosed any information about the woman he had the affair with. This knowledge gap has spurred countless theories online, with Australian radio icon Jackie O weighing in with her own thoughts: that Grohl's baby's mother may be Australian.

"Everyone was shocked when he released a statement. Obviously he had sex with a fan and maybe he didn't know until now. But he was on tour in Australia nine months ago," she revealed.

Grohl was touring with the Foo Fighters in Australia in late November 2023, playing shows in Perth, Adelaide, Melbourne, Sydney and Brisbane.

"It could be an Australian girl because he said he recently became a father. It could be Australian if [the baby was born] just now," Jackie O explained.

Jackie O has a theory. Image: Instagram/Getty

However Kyle, her co-host, not one to buy into the theory, said that he did go to Abu Dhabi, the US and New Zealand after that. "It could be any number of countries," he said.

However, Jackie O's theory was shared by many fans online.

"Which one of you Australians was it?!" one X user posted, alongside the Foo Fighter's 2023 Australian tour dates.

"Is his baby mama in Adelaide?" laughed one fan on Twitter, with another chiming in: "Can you imagine!"

It's not just fans online who are speculating, with gossip site DeuxMoi getting multiple 'blind items' about the musician's love life.

In September 2023, per the Irish Star, the account shared the following post, "This frontman aka nice guy that was once in the most popular 90s band of all time isn't the perfect guy you think he is. I've known him to have a muse/lover for years,."

Despite the speculation, there's no denying this is a difficult time for Grohl and his wife. People have reported that he has obtained a divorce lawyer, despite his Instagram post making it clear that he hoped for a resolution of this conflict in his marriage.

Blum and Grohl at Wimbledon in June. Image: Getty

Until now, Grohl and his wife Blum have appeared to be very much in love. They were last spotted together in June, dressed to the nines as they took in the scenes at Wimbledon in London.

Grohl has previously been open about his love for his wife, sharing the story of how they first met in interviews, and nearly didn't move forward with the relationship.

"When I first met my wife, we went out on a few dates and I decided that I wasn't ready for a serious relationship, so I just stopped calling," he shared.

However, he soon realised his error.

"After three months, I had a revelation and called her back. She picked up the phone and said, 'Oh, I never thought I'd hear from you again'," he recalled.

Blum is yet to make a statement of her own on the matter.

Featured image: Getty