Katharine McPhee Jokingly Tells Fiancé David Foster's Daughter 'Mommy and Daddy Need Alone Time'

Katharine McPhee and David Foster are basking in engagement bliss.

The couple, who got engaged in Italy, took a romantic trip to Stuart Island, British Columbia, where the 34-year-old singer shared a photo of herself sitting in the sun with the mountains in the backdrop.

“Country album drops this week. 🍂,” McPhee captioned her picture, which caught the attention of Foster’s daughter, Erin.

“FEELS LIKE I COULD HAVE BEEN INVITED ON THIS BEAUTIFUL TRIP,” the Barely Famous reality star, 36, wrote in the comments section of McPhee’s photo.

The American Idol alum jokingly responded to her soon-to-be daughter-in-law, writing, “@erinfoster mommy and daddy need alone time,” along with a laughing emoji, face palm emoji and shrugging emoji.

This isn’t the first time Erin has called McPhee her mother or parent.

In early July, Erin teased her father David about his engagement to McPhee when she left a comment on his Instagram post calling McPhee, “Mommmyyy.”

RELATED VIDEO: They’re Engaged! David Foster Proposes to Katharine McPhee During Romantic Italian Getaway

Her comment, first captured by popular Instagram account Comments by Celebs, came shortly after David and McPhee confirmed the news of their engagement on social media.

David’s other daughter Sara, 37, also got in on the laughs, writing, “Out of the country. What did I miss?”

Back in September 2017, as rumors of Katharine and David’s romance circulated, Erin shared a photo of them on her Instagram Stories, writing, “Excited about my new step mom,” and “My parents.”

At the time, a source close to David denied his romance with McPhee as another insider explained that “Erin’s quite obviously tongue-in-cheek and sarcastic Instagram comments were pointed at those who can’t seem to grasp that her dad and Kat can be colleagues, collaborators and longtime friends without it being some big romance.”

“They can’t even perform together without people saying they’re headed down the aisle,” the source said. “Erin was messing with people who jump to conclusions.”

But Erin herself wasn’t denying it.

A month later, in October, she opened up about her dad’s then-girlfriend on the red carpet of the BLEUSALT Launch Celebration in Malibu.

“She’s amazing. I really like her. She’s awesome,” Erin told PEOPLE of McPhee.

“My dad is kind of a hopeless romantic, and Katharine’s awesome. We really, really like her, and we’ve known her for a really long time. And if he’s happy, we’re happy,” she said.

After months of keeping their relationship low key, the couple went public with their romance when they stepped out together at the 2018 Met Gala.