Kate Middleton and Meghan Markle are devoted wives to their husbands, but they don’t always join Prince William and Prince Harry on their trips abroad.

Kara Godfrey, a journalist for Express, that this is because the Duchess of Cambridge and Duchess of Sussex join their husbands on their tour depending on the purpose of the trip.

For instance, Middleton has a slew of charities that she’s involved with. Her husband has chosen to fight against the illegal wildlife trade, and this is something that he works on by himself. But Middleton and Prince William have been actively involved in their Heads Together campaign.

Christina Reeves, a royal expert, said, “Typically William has always worked solo in his fight against illegal wildlife trade, which is why we wouldn’t see Kate join him on a trip like this or him joining Kate on her own personal projects, such as promoting the importance of perinatal, maternal, and children’s mental health.”

Meanwhile, Markle didn’t also join Prince Harry on this trip to Botswana last month. The Duke of Sussex attended a meeting for the Rhino Conservation Botswana, a solo project that he is a patron of. Since it was a solo working trip, Prince Harry didn’t bring his wife along with him.

But two weeks ago, Markle launched her cookbook with the Grenfell survivors to help raise money for the Hubb Community Kitchen. The Duchess of Sussex was joined by Prince Harry, who wasn’t supposed to be there, as well as her mom Doria Ragland. Prince Harry made it to the launch because it took place in London and not in another country.

In related news, Prince Harry and Markle will go on their first overseas tour together to Australia, New Zealand, Fiji, and the Kingdom of Tonga next month. Their 16-day trip will kick off at the Invictus Games, a Paralympics event organized by Prince Harry.