On Friday, McPhee, 35, shared an impressive clip of herself belting out the tune while on an elliptical machine.
“Listen to meeee gee wiiiizzzz,” McPhee captioned the clip. “I’m singing a new little secret song that David wrote for something special during my vocal exercises with @amychapman — Don’t Judge me! 😬🙏🏼”
For her musical exercise, McPhee wore a t-shirt, jean shorts and white sandals.
While she managed to hold the note throughout the clip, McPhee was visibly and understandably out of breath as she fanned herself and yelled out, “Oh Jesus.”
Nonetheless, she finished strong crooning the final lyrics.
The post prompted a number of her followers to praise her with one writing, “We can barely stand and sing, let alone do cardio AND sing!”
Real Housewives of Beverly Hills star Lisa Rinna commented, “You are a 🎁”
Long before he gave her his new songs to sing, Foster knew there was something very special about McPhee.
The couple met for the first time on the set of American Idol during the show’s fifth season in 2006, while he was a guest mentor.
Their interaction was particularly serendipitous, as the Grammy-winning songwriter, 69, seemed to notice his future wife’s talents immediately — and was even captured on film making it known.
During the meeting, the producer confidently told cameras, “Katharine’s got a great, great future ahead of her.”
Foster and McPhee tied the knot last month in London at the Church of Saint Yeghiche in South Kensington, where the bride wore a wedding gown by Zac Posen and the groom wore a tuxedo by Stefano Ricci.
Around 150 guests including designer Posen, as well as close family and friends, were in attendance. All of Foster’s kids were on hand including eldest daughter Amy, who recently revealed she was diagnosed with breast cancer and will undergo a double mastectomy operation.
This is the second marriage for McPhee and fifth marriage for Foster, who was most recently married to Real Housewives of Beverly Hills star Yolanda Hadid after ex-wives B.J. Cook, Rebecca Dyer and Linda Thompson.
Following the wedding, the couple jetted off to Italy for a magical honeymoon.