Duffy, 71, revealed he and Perl, 65, are dating after they reconnected during the coronavirus lockdown and eventually quarantined together.
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"I'm in an incredibly happy relationship," he told People. "I never thought for a minute this would happen again. I never thought I'd feel this way again."
The veteran actor was married to Carlyn Rosser for over four decades before her death from cancer in January 2017. The couple had two sons together -- Padraic, 46, and Conor, 40.
"My wife and I, in 48 years we were always together," Duffy explained, adding that he had resolved to life his life as a widower and focus on his grandchildren.
However, when the pandemic hit, a group text chain brought Duffy and Perl together again after they had lost touch as friends over the years. Eventually, the pair began communicating with just each other. Duffy then took drastic measures to ensure the blossoming feelings were bona fide.
"I loaded up my car and drove 20 hours and ended up on her doorstep just to see if it was real," he explained. "We haven't been apart since."
Duffy believes his late wife would give her blessing on the new relationship.
"I feel quite honestly, that it is keeping with the desires of my wife, the fact that we are intended to be happy," he said. "So when it's offered, think about it, do whatever you do, but don't let it pass you up if it's the right thing."
Starring in the original "Dallas" through its initial 1978 to 1991 run, Duffy would go on to be a part of the soap's reboot from 2012 to 2014. He also starred in the sitcom "Step by Step" from 1991 to 1998.
Purl was best known role for her role as Ashley Pfister on "Happy Days" from 1982 to 1983. She has been married four times with the last marriage ending in 2011.