She opened up about their airplane tryst nearly ten years ago.
Two weeks after she was forced to defend herself over leaked information regarding her enjoyment of female escorts while on her 'Sheezus' tour, Lily Allen opens up about sleeping with a married Liam Gallagher almost ten years ago in her newly released autobiography.
Lily Allen performing at Way Out West
The 33-year-old revealed that she and the former Oasis frontman became fully-fledged members of the mile-high club in 2009 when they were on a flight to Japan together for the Fuji Rock Festival. Lily claimed they got drunk and ended up having a moment of passion in the bathroom.
'We got hammered on the plane. At some point Liam and I found ourselves together in the toilet doing something that he shouldn't have been doing, and it wasn't drugs', she wrote in her new book 'My Thoughts Exactly'. 'Then we were in a lie-down bed together.'
Indeed, the Manchester icon - was is twelve years her senior - invited her to his hotel room when they touched down in Tokyo, and it was only the following morning she realised he was actually married to Nicole Appleton.
'It wasn't until the next day when he said something like, 'No one can hear about this because of Nic', that I clocked he was married', she said. 'I knew Noel was married and I knew Liam had been married to Patsy Kensit. That was partly why I fancied him. I'd grown up an Oasis fan. I was 12 when he and Patsy Kensit were on the cover of Vanity Fair as the coolest couple.'
Their romp took place the year after Liam and Nicole got married, and the year before Liam began an affair with New York Times journalist Liza Ghorbani, with whom he fathered a daughter named Gemma.
While Liam's moment with Lily did not serve to end his marriage, Nicole did end up finding out about it six months later. Liam ending up calling Lily on the phone trying to convince her to lie, and she hinted that she obliged.
'He sounded awful, like he'd been up all night', she said. '[He said] I just need you to get on the phone. I've got Nic here. One of your mates is, like, trying to do a wind-up or something and saying that you and me had it off or whatever, and I need you to speak to Nic and say that it's all b*****ks.'
'Oh, Liam, yes sure, it's all b*****ks', she continued. 'Let's say it's all b*****ks - of course I'll tell Nicole that it's all b*****ks if that's what you want - and not think about it too much or even at all, and then maybe it will go away and not disrupt what really matters: The people we love and rely on.'
Liam is yet to comment on Lily's book claims, though if the mouthy rocker can remain silent on the subject permanently we'd be very much surprised.
'My Thoughts Exactly' by Lily Allen will be released on September 20th 2018.