The reality TV star, who proposed to Mecklenburgh during filming of TOWIE's Marbella special this summer, suggested that his scepticism came from Argent being "ashamed" of dating someone "completely opposite" to his "stunning, beautiful" ex Lydia Bright.
"Well, when they first got together, Lucy and I were the first to say, 'That's not real'," he told New. "But away from the cameras... they genuinely looked loved up.
"I think he does love her. Where before he used to be with Lydia, and she is a stunning, beautiful girl, Gemma is the complete opposite. I think Arg was almost a little bit ashamed. It's a shame. He is better than that."
Falcone also addressed his own relationship with Mecklenburgh, saying that his partner has earned his trust after being "naive and immature" when they were first dating.
On whether persistent rumours of him cheating damage their romance, he declared: "If anything, it makes us stronger. We're engaged. We're happy. I come home to her every night.
"[I trust her] 100 per cent. I think she was naive and immature but now she's moved in with me and she's grown up."
The Only Way Is Essex continues Wednesdays and Sundays on ITV2.
Watch Mark Wright discuss Arg below: