Katharine McPhee jokingly trolls future step-daughter Erin Foster

Katharine McPhee, 34, and fiance David Foster, 68, have been busy posting photos from their vacation in Stuart Island, British Columbia. 

And on Tuesday, David’s daughter, Erin Foster, 36, made it clear that she would have happily tagged along. 

‘FEELS LIKE I COULD HAVE BEEN INVITED ON THIS BEAUTIFUL TRIP,’ she commented on one of McPhee’s snaps. 

This led Katharine to jokingly troll her soon-to-be daughter-in-law. 

‘Mommy and daddy needed some alone time,’ the singer quipped. 

Tommy Haas—Erin Foster’s brother-in-law—also chimed in on the thread. 

‘@erinfoster always looking to be the fifth wheel #worm,’ he wrote.  

Foster, unmarried, responded: ‘I’m a great addition to any relationship.’

‘FEELS LIKE I COULD HAVE BEEN INVITED ON THIS BEAUTIFUL TRIP,’ David’s daughter, Erin Foster, commented on one McPhee’s snaps 

This led Katharine to jokingly troll her soon-to-be daughter-in-law. ‘Mommy and daddy need alone time,’ the singer quipped

Tommy Haas—Erin Foster’s brother-in-law—also chimed in on the thread. ‘@erinfoster always looking to be the fifth wheel #worm,’ he wrote

David Foster, who’s been married four times, is a father to seven children. 

McPhee is three years older than his youngest child—Jordan, 31. 

Katharine and David became engaged back in July after roughly a year of dating.

Fifth times the charm: David Foster has been married four times. The couple became engaged back in July after roughly a year of dating

In a recent interview with E! News, David’s daughter, Sara Foster, 37, weighed in on the pending marriage. 

‘My dad loves love. My dad loves commitment, he’s always been married. He’s never been single really,’ she said. ‘I’m happy for him, he’s really happy. She’s wonderful. She’s a great addition [to the family].’ 

In a recent interview with E! News, David’s daughter, Sara Foster, 37, weighed in on the pending marriage. ‘My dad loves love. He’s never been single really,’ she said. ‘I’m happy for him. She’s a great addition [to the family].’

David Foster Harbour Pathway: Katharine kicked off her shoes so she could be hoisted up for a photo by her fiance 

Katharine also stole headlines on Tuesday when she attempted to promote voter registration for the upcoming midterm elections. 

‘Voting matters,’ she tweeted alongside a photo of herself with American Idol winner, Taylor Hicks, who beat her out for the season five title back in 2006.  

Shade thrown! On Tuesday, McPhee attempted to promote voter registration for the upcoming midterm elections. ‘Voting matters,’ she tweeted alongside a photo of herself with American Idol winner, Taylor Hicks, who beat her out for the season five title back in 2006