Taking to Instagram last night (17 May), Lydia shared a photo of herself and Arg celebrating his latest achievement.
Writing alongside their selfie, she said: "Sheesh Sunday's celebrating Args charity trek. Dad photobombing #ProudGirlfriend."
In her photo, Lydia looks totally gorgeous smiling alongside Arg with a glass of celebratory champers in her hand. And despite his gruelling mountain climb, Arg still had a big grin on his face as he spent the evening with his girl.
Lydia's photo comes after Arg completed a 50km trek across 3000ft high Snowdonia in Wales within 24 hours, starting at 6am on Saturday morning.
Raising money for mental health charity, Mind, Arg joined fellow celebs Gail Porter, Matt Johnson, Nicholas Pinnock and Anna Williamson.
Speaking about his charity challenge, the Essex boy said: "Over the past few months I've realised how important it is to have support around you when you're going through a tough time... Things have been hard for me lately but I feel exceptionally lucky – I have come through the other side with the love and care of those close to me. Now I want to help make sure other people can do the same."
Last year, Arg was suspended from The Only Way Is Essex after a bout of excessive partying.
Following his suspension, the star suffered with anxiety and depression and voluntarily checked himself into rehab over the Christmas period to seek treatment.
Since his rehab stay, Arg has returned to TOWIE and is visibly healthier and happier following his lifestyle overhaul. Not only has he improved his own wellbeing, but the 27-year-old has now reunited with childhood sweetheart Lydia, after the couple went through a tough time.
Wiping the slate clean, Lydia and Arg decided to give their on/off relationship another go in April, claiming this time their love story is forever.
And proving they're not messing about this time round, the couple recently announced they are now living together!
Lydia revealed she had asked Arg to move in with her and her co-star beau couldn't be happier. Speaking about his girlfriend, he said: "You only get one true love and I do think Lydia is my soul mate. She's my best friend. Neither of us can imagine being with anyone else."
To find out more about Mind and the Mind 3000s trek, click here.
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