McPhee and the 31-year-old British actor were reportedly caught kissing between takes on the Los Angeles set of their new CBS series in August. The couple's PDA was also photographed when McPhee kissed her man on the cheek and flirtatiously grabbed his butt, according to Us.
An insider told the magazine that McPhee and Gabel "were inseparable and got cozy all night" at the private premiere for Scorpion in Hollywood on September 22. The couple had been joined at Warwick nightclub by the rest of their cast and some friends.
The budding relationship comes almost one year after McPhee was caught making out in a parking lot with Morris, who claimed to have been ashamed of cheating on actress Mary McCormack, his wife of 10 years and the mother of his three daughters.
"He is devastated he has caused so much hurt," a source told Life & Style in October 2013. "He doesn't want to throw his perfect family away for the sake of a fling with someone who didn't mean anything to him."
McPhee was also still technically married at the time of her Morris fling. She tied the knot with Nick Cokas, 49, in 2008 but had reportedly been separated from him for about six months when the kissing incident occurred.
While McCormack allegedly took Morris back after briefly kicking him out of the family home, McPhee's marriage ended. She filed for divorce from Cokas after six years of marriage in May.
However, a representative for the actress told Us that McPhee and Cokas still "have an amicable relationship and will remain friends."