Bill and Melinda Gates waited until their youngest daughter turned 18 before they announced divorce, reports say

• Bill and Melinda Gates announced on Monday they were divorcing.
• A source told People the timing related to their youngest daughter finishing high school.
• They also said a "combo of things" led to the split rather than one main reason.

New details have emerged about the timing of the divorce of one of the world's richest couples, Bill and Melinda Gates.

The pair, who were married for 27 years and have three kids, lead a foundation focused on philanthropy, which has a $49.8 billion endowment.

It's unclear what the main causes of the split were but People said a source revealed details about the timing.

The source told the outlet: "The decision to part ways appears seems to be linked to their youngest daughter, Phoebe, turning 18 years old. "It's absolutely because their youngest child is graduating from high school, and the idea was that they stayed together through that."

They added: "They limped through until their kids were out of school like a lot of people."

The couple released a joint statement on Monday to announce their split.

"After a great deal of thought and a lot of work on our relationship, we have made the decision to end our marriage. Over the last 27 years, we have raised three incredible children and built a foundation that works all over the world to enable all people to lead healthy, productive lives," it said.

The couple's eldest daughter Jennifer took to Instagram, following the announcement. "It's been a challenging stretch of time for our whole family. I'm still learning how to best support my own process and emotions as well as my family members at this time and am grateful for the space to do so," she wrote.

Asked whether the divorce will get more get disputatious, the source told People it is not likely.

Bill Gates, is worth $146 billion and is the fourth-richest person in the world, according to the Bloomberg Billionaires Index.