AceShowbiz - Actress Sara Foster wasn't surprised to discover her dad David was dating a woman half his age, because her friends have always found the music producer attractive.

David Foster, 68, popped the question to singer/actress Katharine McPhee, 34, during a romantic vacation in Capri, Italy in early July after just over a year of dating, and she has already been warmly welcomed into the family by his daughters Sara, Erin, and Amy.

They have even enjoyed joking about having Katharine as their new stepmother, even though they are so close in age, but Sara insists that has never been a real issue for the girls.

"His essence and his aura is that of like, a 40 year old," she told Us Weekly of her father's youthful nature. "My 30-year-old friends have always wanted to date him. Always!"

Laughing about his ability to stay "forever young", Sara claimed the age difference between her dad and his bride-to-be "means nothing," urging critics to "mind their own business".

"People need to just get over it," she added.

Sara's remarks emerge a month after her musician sister Amy revealed David and Katharine are "perfect" for one another.

"All I can tell you is it absolutely works when you see them together. It's love," she gushed. "The haters (can) shut the f**k up because they are perfect for each other."

The backlash was so intense when the couple first announced plans to wed, Katharine herself took to social media to shut down her detractors.

"Y'all should be worrying more about registering to vote and midterm elections than who's marrying me," she fired back at her Twitter haters at the time.

The marriage will be Foster's fifth. His ex-wives include Linda Thompson, B.J. Cook, and model Yolanda Hadid, who he divorced in October (17).

Meanwhile, McPhee wed Nick Cokas in 2008. They divorced in 2016.