David Foster's Daughter Erin Foster Calls Katharine McPhee 'New Stepmom' On Instagram

David Foster and Katharine McPhee's romance may be getting serious.

On Tuesday, Foster's daughter, Erin Foster, shared a snapshot of him and the "American Idol" alum at the Grammy Museum Gala honoring him, Us Weekly reported. In her post, Erin, 35, may have hinted that McPhee, 33, will soon join their family as she captioned the photo: "Excited about my new step mom." In the photo, McPhee sports a low-cut black dress and has her hair slicked back as she chats with the "Asia's Got Talent" judge.

Erin also shared a clip via Instagram story showing McPhee and her dad by the piano and once again alluded to their relationship. "My parents," Erin wrote in the caption.

Foster and McPhee have been plagued with dating rumors since May. At the time, the pair was spotted at Nobu in Malibu enjoying a dinner date. They were seated at a private, sea-front table in a corner and were reportedly very sweet to each other during their date.

"David and Katharine were very intimate during their dinner," an onlooker told E! News. "David was seen grabbing Katharine's face and kissing her cheek several times. Katharine was doing the same to David's face and they were acting as if they were a couple."

The source added that the pair shared two bottles of red wine and ordered various sushi dishes. They apparently spent less than two hours in the restaurant and left together in an Uber. "By the end of the date, Katharine sat on David's side of the table and cuddled him with a blanket," the insider added.

In related news, while her father is reportedly in a relationship with McPhee, Erin is apparently the object of John Mayer's affections. Mayer made his interest known when Foster shared a photo of himself and Erin on Instagram and greeted the latter on her birthday. "One of the loves of my life and my fav daughter on this day!!! Happy bday @erinfoster #iloveyou," the Canadian musician wrote in the caption.

To the surprise of many, Katy Perry's ex commented on the photo, asking Foster to set him up with his daughter. "Can you put a good word in for me?" the singer wrote.

Unfortunately, none of the Foster family responded to him. He announced on July in a tweet that he is still single.

"Hi girls I'm John, single, I wear a patch for back pain and have a daily phone alarm set to remind me to take antacid. Real bad boy type," he wrote on Twitter.

What can you say about Erin's posts about McPhee and David? Drop a comment below.