The 22-year-old actor, who plays antiques shop manager Anthony Moon, immediately hit it off with McGarty, who plays teenager Whitney Dean, reports the Daily Mail.
He told Closer: "I had seen Shona on TV and always thought she had a gorgeous smile, but it is all about the personality.
"When I met her, we just clicked. It really was love at first sight."
He went on to say that the pair bonded over music, recalling: "I play the guitar and Shona is an amazing singer, so we would hang out in each other's dressing rooms playing songs."
The pair met after Lapinskas joined the show a year ago. McGarty, 20, had been playing Whitney on the show for four years.
It was announced last month that Lapinskas is to exit due to Anthony Moon being written out of the show.
"These things happen. The show has a new executive producer and she wanted to make changes," he said. "I am upset, but EastEnders has been amazing and hopefully it will be a springboard into something new."
Speaking of his post-EastEnders plans, Lapinskas recently expressed his desire to appear as a contestant on Strictly Come Dancing, as well as pursuing a movie career.
Watch a video of Lapinskas on the set of EastEnders below: