While they were able to keep their romance - which began in July 2016 - largely a secret, it quickly became apparent to the actress’ co-stars on the Toronto set of the show that she had a high-profile boyfriend.
“I didn’t think it was happening and then one day, on the set, there was an MI5 guy,” Wendell Pierce, who played her lawyer dad Robert, to KTLA 5.
“There was this MI5 guy on set so I said, ‘well, this must be serious’.”
The actor also revealed how while filming a scene for Suits - which Meghan departed in November 2017 when her engagement was announced - she had to remove a fake engagement ring in case onlookers thought the royal had already proposed.
"Then one time, we were doing a scene before they got engaged where she was engaged with Mike [played by Patrick J. Adams] on the show and they said, ‘wait, don’t get out of the car'," he explained.
"They said, ‘give us the ring because there’s a paparazzi down the street.’ And if the photo got out with the ring..."
Pierce also revealed he had been prepared to tell Harry to treat his on-screen daughter like a princess.
"He came to set one time, the prince - I didn’t get the chance to see him,” he recalled.
"But I was ready to tell him, as the TV dad, ‘you know, you break her heart’ - I was really going to say that but then I didn’t get the chance.”
Meghan, who moved to the UK permanently following the engagement, starred in her final episode of the show in 2018.
Her character was seen getting married to on-screen boyfriend Mike just weeks before the royal wedding in real life.
Many of her co-stars - including Sarah Rafferty, Patrick J. Adams, Gina Torres and Abigail Spencer - attended the Windsor nuptials.
Earlier this year, the show - which Meghan joined in 2011 - made reference to the Duchess’ new life.
Mike was asked by another character how his on-screen wife was getting on.
“If I told you how good, you probably wouldn’t believe me,” he replied.