When Katharine McPhee was 21, she met 56-year-old David Foster. 15 years later, they had a baby.

In 2006, a then 21-year-old Katharine McPhee decided to enter into the iconic singing competition American Idol.

She rose up the ranks and was the runner-up on the fifth season of the show, helping her to cement a career in theatre and music. Along the way though, she met a certain someone while she was a contestant.

And it was David Foster. A renowned composer, record producer and music executive, David and fellow musician extraordinaire Andrea Bocelli were brought onto the show as guests to help coach some of the contestants during their singing practices. 

While David watched Katharine perform Whitney Houston's ballad 'I Have Nothing' – which is actually written by David himself – he praised her singing abilities and said she had a great future ahead of her.

Fast-forward 16 years and the pair are married and have one child together.

Watch the moment where David Foster and Katharine meet on American Idol. Post continues below.

After American Idol, Katharine and David kept in touch and were seen at various events together, sometimes even performing together.

In 2008, Katharine married American actor Nick Cokas – David was at their wedding and even accompanied Katharine on the piano as she performed at their reception. Then in 2014, the couple announced they had decided to split.

As for David, his relationships go as follows: His first marriage was to singer/writer B.J. Cook from 1972 to 1981. David then went on to marry his second wife, Rebecca Dyer, in 1982 and the pair divorced a few years later. 

He married his third wife, actress and beauty pageant queen Linda Thompson, in 1991 and the couple divorced in 2005. It was a relatively high-profile marriage, given David became a stepfather to Linda's two sons – Brody and Brandon Jenner – from her previous relationship with Caitlyn Jenner.

The fourth marriage was also high-profile, as David married Dutch model Yolanda Hadid, who is the mother of the famous model trio Gigi, Bella and Anwar Hadid. The couple were together from 2006 to 2015 and their relationship featured regularly on The Real Housewives of Beverly Hills. When the announcement of their divorce broke, it was quite the shock among celebrity circles. At this point, David had five daughters of his own from his various relationships.

That takes us to 2017 – when Katharine and David began dating.

At the end of that year, the Grammy Museum hosted a gala honouring David, and he brought Katharine as his date. That same night, one of David's daughters posted to her Instagram Stories to confirm her dad's relationship, writing: "Excited about my new stepmom," with a photo of Katharine and David.

Although in an interview a few weeks later, Katharine remained coy about the relationship.

"We're very close friends, and we've been friends for a long time. I'm really, really fond of him, and I think he's an incredible person. I've known him since I was 21 years old, you know? He produced my first single. So he's been really good to me. People can say whatever they want," she said to Health Magazine, referencing the rumours.

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Soon after it was confirmed, they were dating. With a 34-year age-gap, and the fact four of his five daughters are older than Katharine, the tabloids had a field day.

Addressing the age-gap, David said to PEOPLE that the reference is often made with judgement.

"I've always said there's so many things that can bring a marriage or relationship down, and age difference is just one of them. There's so many things that can go wrong. We think we have it pretty together."

By 2018, David had proposed to Katharine.

Just prior to their engagement, Katharine's father had passed away, but before his death, Katharine and David had shared with him their plans to marry.

"My dad was so happy for me. My ring was the last thing I showed my dad before he passed and makes me smile when I look at this as a reminder of our last conversation," she wrote on Instagram with a picture of her engagement ring. "And now I’m ready to share with all of you what has been my sunshine amongst this painful loss. We're celebrating life and not forgetting love."

Soon after the news, the couple went to Italy to perform at a concert alongside Andrea Bocelli. Before they sang 'I Can't Help Falling in Love With You', Andrea said over the microphone to David, "A few years ago, I told you she was the one," to which David responded, "You were right."

In 2019, they married – exactly 13 years after the day Katharine's first single was released. Yes, the one which David produced.

"Life is full of beautiful coincidences, isn't it? Thank you for taking me over the rainbow, David," she said.

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A post shared by Katharine McPhee Foster (@katharinefoster)

In late 2020, they announced they were expecting a child together, and a few weeks later, Katharine gave birth to their son Rennie David Foster.

Reflecting on the name choice, Katharine said: "We picked Rennie because I'd actually been in labor for a while. We didn't have a name picked out. We had a couple names, but my husband was on a text chain with his sisters and one of his sisters suggested an old family name. It was his great-grandfather's name, his great-uncle's name, so it has a long history in his family. My husband said, 'Hi, Ren Foster,' and so we said, 'That's a good name. It's a strong name'.

"It's a growing family, and David's doing great. He's always walking into a room saying, 'Where's my baby? Where's our baby? He wants to hold the baby all the time, and be around the baby."

David now has six children in total, becoming a father to Rennie when he was 71.

While having a baby at this stage of his life was "not something" he thought was on the cards, he said in an interview this week that he "hasn't regretted a single day of it".

"I've loved every single day. It's the standard thing of like, 'Oh, well, you were so young when you had your children, and you were working day and night, you never saw them'. And there is some truth to that, sadly, for my [older] kids. I was just working a lot. I'll cancel anything just to hang with him. It's just different."

On the age-gap realities, Katharine said in the same joint interview that she had always "hoped" to have a baby with David but knew there were "no guarantees" due to age. 

The pair said to PEOPLE "we know we're an unconventional couple" but knew they were the right fit for one another.

"With Céline Dion and [late husband] René Angélil, there was a big age difference, and after I was working with them for a long time it just became Céline and René," David said. "It just looked and felt normal. But it was, of course, kind of odd in the beginning. But I think we're over that hump now with five years of being together, and hopefully people just start looking like we belong together because we feel like we do."

Katharine added: "Even if they don't, we don't care. We just love our history, how we met and where we are now. Sometimes we look at each other like, 'This is so wild that we're together'."

Feature Image: Instagram @davidfoster/@katharinefoster.