Prince Harry is “very likely” to reunite with King Charles and Prince William during his trip back to the UK this month, and may be “testing the waters” for a way back into the royal fold, the monarch’s former butler Grant Harrold has told SkyNews.com.au.

The Duke of Sussex, 40, confirmed he will travel from California to the UK to attend an annual charity event for seriously ill children on September 30.

He will present the recipients of the WellChild Award for Inspirational Children with their accolade in a ceremony and make a speech on stage

Mr Harrold believes Harry’s visit back home could indicate that his frosty relations with Royal Family have begun to thaw, after the firm wished him a happy birthday on social media earlier this month.

“I’m assuming with the birthday message recently that relations have slightly improved, so it’s very likely he will see his father and brother (in the UK),” Harrold said on behalf of SpinGenie.

“But bear in mind this is likely to be done privately behind closed doors, so we would never find out about those discussions or if they take place.

“I’d like to think that there most likely will be an opportunity for him to catch up with his family.”

The insider believes the 75-year-old King will “make time” to meet with his youngest son, in what would be their second reunion in person this year since February.

The Duke failed to reunite with his father when he again visited home in May for the 10th anniversary of his Invictus Games foundation.