The former TOWIE star, 23, showed her love for boyfriend Louis in Montpellier as he competed in the pommel horse final at the prestigious sporting event.
As Louis took gold, Lucy shared a picture of the amazing moment with the message: "My baby getting his Gold Medal #Euros2015 #Gymnastics #Pommel @louissmith1989."
Lucy had been by Louis' side in the French city as the competition took place and was rewarded when he came top of the leaderboard.
Louis, 25, was competing for Britain for the first time since London 2012 after coming out of retirement ahead of the 2016 Olympics in Rio.
He and fellow Brit Kristian Thomas both won gold. For Louis, it was his first gold after previously winning two Olympic medals on pommel - bronze in Beijing in 2008 and silver at London 2012.
After he was presented with his medal, Louis gallantly handed Lucy his winning bouquet.
Sharing a stunning selfie holding the flowers, Lucy gushed: "Awee @louissmith1989 gave me his flowers from the medal presentation #Euros2015#Gymnastics."
He in turn tweeted: "Aw @lucy_meck thank you so much for being here. I would have given you my chocolates too but I know your on a diet lol. Safe flight babe's x."
Fitness fanatics Louis and Lucy confirmed they were dating in January after meeting on BBC1 TV show Tumble.
Strictly champion Louis recently told Reveal: "I haven't felt like this for a long time, if ever. It's taken me by surprise.
"Lucy is just so lovely which is rare to find in someone who looks as beautiful as her. I've been on dates with girls who are gorgeous - but they know it."
He also admitted they have talked about marriage and babies!
What has Lucy Mecklenburgh been up to since TOWIE?
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