Katharine McPhee and David Foster Open Up About Their Love

"It doesn't make sense to a lot of people, but it does to us," Katharine McPhee, 34, tells PEOPLE of her romance with David Foster, 68, in this week's issue.

Katharine McPhee and David Foster have tunnel vision when it comes to their relationship. Their focus is on one another.

That connection was on full display during Celebrity Fight Night in Italy on Sunday, where McPhee performed “I Can’t Help Falling In Love with You” with Andrea Bocelli and barely took her eyes off of Foster, who accompanied on piano.

“A few years ago I told you she was the one,” Bocelli told Foster just before the duet, to which he responded, “You were right.”

The luxurious weekend-long charity event, which raises funds for the Barrow Neurological Institute and the Muhammad Ali Parkinson Center, nearly doubled as an engagement celebration for the pair. After dodging relationship rumors for months, they confirmed in July that Foster had proposed with a sparkling emerald-cut diamond ring while they vacationed in Anacapri, Italy.

David Foster and Katharine McPhee.

Opening up for the first time in this week’s issue, the hit-making musician, 68, and former Smash star, 34, tell PEOPLE that despite their 34-year age difference (which has spurred a number of lighthearted jokes between McPhee and his daughters Sara, 37, and Erin, 35) they’re much more focused on all that they have in common.

“We genuinely love and respect each other and have for a very long time,” says McPhee. The pair first met in 2006 when Foster mentored her and other contestants on Season 5 of American Idol.

“She didn’t catch my eye on the first day because I was so busy trying to do my job,” says Foster, who went on to produce McPhee’s first single. “But,” he adds, “the reality is that in the last 12 years I’ve always had a connection with her.”

Katharine McPhee and David Foster. Jason Merritt/Radarpics/Shutterstock

What began “on a friend basis” says McPhee, later transformed into a romance that took them both by surprise. “There are just a lot of things when you look at the history of our relationship, neither of us could have written it. I would never have imagined that this would be our future together.”

As for what bonds them, “the fact that we are both in the music industry helps,” says Foster, who recently embarked on his The Hitman Tour. McPhee recently wrapped her run in Broadway’s Waitress. “We understand each other,” he says.

RELATED VIDEO: David Foster Talks Katharine McPhee’s “Waitress” Debut: “She’s the New Belle of Broadway”

And while they know their significant age gap has been a hot topic, they’re tuning out the noise. “It doesn’t make sense to a lot of people, but it does to us,” McPhee says of their love.

And they’ve got the full support of his daughters, who have fun making jokes, but both “love” McPhee, a source previously told PEOPLE.

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Now in the midst of planning what will be Foster’s fifth marriage (he divorced Yolanda Hadid in 2017) and McPhee’s second (she divorced Nick Cokas in 2016), the couple is banking on forever.

“He has things to learn from me and I have a lot of things to learn from him,” says McPhee, “so I think we have a nice yin and yang.”

For more on David Foster and Katharine McPhee’s Romance, pick up this week’s issue of PEOPLE, on newsstands Friday.