Prince Harry and his sister-in-law Kate Middleton, the Duchess of Cambridge’s sister, Pippa Middleton, have reportedly been carrying on an unlikely romance.

In a new report from OK! Magazine, sources say Middleton and Prince Harry have been seeing each other in secret for months.

When Middleton became single after her split from Nico Jackson, she reportedly began spending time with Prince Harry. “They’re trying to play it coy, but there’s no doubt that this is developing into something serious,” the source said. “They’re truly sweet together and, in fact, seem very much in love.”

According to Magic, there’s rumors Duchess Kate caught her sister kissing her brother-in-law at her wedding to Prince William in 2011. She was reportedly against the couple being together, so they didn’t pursue it at the time.

In May, Prince Harry talked about his desire to settle down. "It would be great to have someone else next to me to share the pressure,” he said of royal engagements.