Mary, who owns Borchardt restaurant in Berlin and on his fourth marriage, reportedly "doesn't mind" his much-younger wife dating the Hollywood actor.
"They are still married, but you could describe their relationship as an 'open marriage,' a source told the Daily Mail.
"He has been married several times and has five children. He is not interested in negativity or jealousy."
According to reports, the model first met Pitt at her husband's restaurant while he was there promoting his film Once Upon a Time in Hollywood.
Poturalksi then flew to Los Angeles a few weeks later to meet up with Pitt again. They were photographed attending a Kanye West concert in November.
Last week Pitt was spotted arriving in France on a private jet with his rumoured new love interest.
The 56-year-old Oscar-winning actor, who split from his wife Angelina Jolie in 2016, and the German model were said to look like "loved-up teenagers" after being photographed together for the first time at an airport in the south of France, according to The Sun.
The pair were seen departing a private jet at the Le Castellet Airport, after Pitt had reportedly flown from Los Angeles to Paris to meet up with Poturalski.
"They were kissing and Brad was being super attentive to her," a source told OK! magazine.
"He was in a semi-public place but didn't seem to mind people seeing him. She's a real beauty and obviously a lot younger than him."
Poturalski also bears a striking resemblance to Jolie, 45.
Reports suggest Poturalski and Pitt are spending time together at Pitt's lavish holiday home Chateau Miraval, a vineyard estate he bought for $67 million in 2011 with Jolie.
Boasting over 100,000 Instagram followers, the Berlin-based Poturalski has also been an ELLE magazine cover girl and is managed by A Management modelling agency.
It comes as Pitt and Jolie continue with their messy divorce which has been dragging on longer than their two-year marriage (although they dated for a decade before they wed).
The latest twist in the ongoing saga, which heightened the sheer intensity of their feud, was the revelation that their six children – Maddox, 19, Pax, 16, Zahara, 15, Shiloh, 14, and 12-year-old twins Vivienne and Knox – were absent from Pitt's mother's recent 80th birthday bash at the Fight Club star's Santa Barbara beach house in California.
Sources close to the family said Pitt's parents, Jane and William, hadn't seen their grandchildren for more than four years.
Jolie has reportedly delayed the child custody settlement by trying to get the judge presiding over the case removed.
She is said to have raised concerns over John W. Ouderkirk's lack of transparency concerning previous cases he was hired for involving Brad's lawyer Anne C. Kiley.
Jolie believes Mr Ouderkirk's close connection with Ms Kiley may give her ex-husband an advantage.
