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"My forever Valentine! My best friend, my favourite person, my motivator, my everyday! David Foster I love you, cookie. #happyvalentinesday," McPhee wrote on Instagram, alongside a throwback photo of herself and Foster loved up on the beach.
The couple's 35 year age difference has been a controversial topic since the pair began dating back in 2017, and trolls still never miss an opportunity to take jabs at their relationship. Unfortunately, this time was no different.
One person sounded off on the photo, accusing McPhee of only marrying Foster for his money, to which she hilariously clapped back at with the perfect reply.
"There for the money," the troll commented. "Obviously," McPhee quipped, not letting the haters get to her.
In case you missed it, McPhee revealed in October that she and Foster are expecting their first baby together, after she was spotted shopping for baby supplies.
While this will be the "Smash" actress's first child, Foster already fathers five children from his previous marriages: Allison, 50, Amy, 46, Sara, 39, Erin, 38 and Jordan, 34.
In an interview with People in July, Foster's daughter, Erin opened up about what it has been like having McPhee join their family.
"Our biggest issue with [Katharine] is how hot she is," she joked. "Her body is insane. When she comes over for family Sundays, I'm like, 'Do not get in a bikini.' My husband's always like, 'Kat, get in the pool!' And I'm like, 'Simon...'"
Erin also revealed that McPhee has been a positive influence in their father's life by helping Foster become more in touch with his feelings.
"Interestingly, the age difference has played a role in a positive way," Erin explained. "Our dad comes from a generation where women are more passive. He is also passive about his feelings. Kat has really pushed him to open up.We could get into a fight, and then Kat's like, 'No, you have to pick up the phone, call your daughter back.' She's a facilitator, which is really important. She pushes him to be more emotional and more vulnerable."