They rekindled their romance earlier this year after a lengthy break.
The former Love Island star, 29, showed off her endless pins in a racy white dress as she joined the former TOWIE star, 26, at the event.
Megan and Demi rekinded their relationship in February, and have taken their romance long distance after the Sims sisters relocated to LA.
The reality star flaunted her famous curves in her tight white dress with ruché detailing that accentuated her ample cleavage.
Megan accessorised her look with a matching cross-body handbag and heels as she arrived for the opening.
Megan played coy when asked about the pair's rekindled relationship, telling MailOnline: 'It’s just a girls night. Just a fun girls night for us.'
Meanwhile Demi showed off her edgy fashion sense by opting for a bold grey denim crop top and matching jeans.
The star completed her outfit with metallic silver heels and a simple handbag.
Demi told MailOnline she is only back on home turf for a short period and will jet back to LA soon to film her family reality show House of Sims.
She said: 'I go back out to LA next week to continue filming the reality show I’m back and fourth at the minute.'
Back in February, Demi confirmed she had rekindled her romance with her former flame Megan after splitting up two years ago.
The former TOWIE star revealed she is 'buzzing' to have the star back in her life and is looking forward to seeing what the future holds.
Demi detailed how the pair met for the first time in years at a racy OnlyFans shoot and she 'knew from that moment we were going to get things back on'.
Speaking to Scott McGlynn on his Celebrity Skin Talk Show, the reality star admitted she 'could sense' there was still feelings between the pair during the lingerie shoot.
She said: 'So me and Meg, obviously we were seeing each other a few years ago. But we were working on a show and we were in a rush.
'It wasn't how you would normally go about a relationship. Then it ended, and we always had this connection whether it was friendly or a bit more, even if it was friendly we'd have phone calls, we'd disappear and then we'd talk to each other.'
Demi continued: 'Then I came back to England and I was doing a photoshoot with her with OnlyFans, and she's standing there in her lingerie, and I'm like "Omg what is going on".
'I'm trying to play it cool as I'm getting into my lingerie. It's hard when two exes are standing there in our lingerie. We both smiled at each other and I could sense it, I could tell.
'We had to stand nose to nose and hold each other, and it was just one of those moments when you can feel the energy. I just knew we were going to get things back on.'
Last year Demi moved to Los Angeles to film her own reality TV show, House of Sims, with her family for OnlyFans.
Despite living across the pond and being temporarily back in the UK, the TV personality confirmed she will continue seeing Megan regardless of the distance.
Demi said: 'We need to have a conversation now because I live in LA, but she is hopefully going to come and visit me.
'I'm not saying I want to get back into a relationship but for someone to come back into my life it has been nice.'
The reality star even told Scott about her Valentine's Day, she added: 'We've not made any plans so far but I'm seeing her in two days, we're going for dinner so we will discuss it then.'
Demi and Megan first struck up a romance on E4's Celebs Go Dating in 2019 but after just a few months they went their separate ways.
Megan went onto admit that Demi made her question if she was actually gay or not and said they had no 'sexual chemistry'.
Back in October 2019, Demi revealed to MailOnline that Megan had apologised for saying there was 'no sexual chemistry'.
She said at the time: 'I unblocked her because I wanted to know what she had to say and she kindly apologised for everything she had done.
'She knew she was in the wrong with everything she had done to me. She apologised and we wished each other the best. I was really shocked because I didn't expect her to ever apologise.
'It felt really nice and it made my heart warm a bit more. I had a bitter frost towards her because of everything she did to me but when she apologised, it made everything better.'Read more 2023-06-09T04:06:56Z dg43tfdfdgfd