The 35-year-old former "American Idol" contestant performed alongside the 69-year-old during a cruise to Provincetown, Massachusetts which kicked off at the weekend (August 11), where he and the singer addressed the negative comments their relationship has attracted.
"I don't know if you noticed or not, but there's a bit of an age difference between the two of us," Foster reportedly told the crowd, according to Page Six, "But on this cruise, nobody gives a s **t."
According to the outlet, McPhee then also addressed those criticising the relationship, adding "Go f **k yourself."
The couple wed in a ceremony last June (18). This is the second marriage for McPhee and the fifth for Foster, who has six children from his previous relationships, including Erin Foster, 36, and Sara Foster, 38, who have both poked fun at their stepmother's age on social media.
Last year, Sara took to Instagram to share a photo of her and the brunette beauty posing in skimpy bikinis.
"When your mom refuses to dress age appropriately," she jokingly captioned the shot.
In another post, McPhee shared a shot of herself lounging at the pool sporting a similarly sexy look, which prompted a funny comment from Erin.
"Grandma!!!! WTF (What the f**k) I don't want to be next to you at the pool," she wrote.