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Prince Harry dramatically upped the ante in his war with the royal family Friday as he upstaged his estranged brother Prince William by making a shock visit to his grandmother Queen Elizabeth II’s grave on the first anniversary of her death.

He was snapped by a member of the public emerging from St. George’s Chapel in Windsor Castle, where the late queen is buried, just minutes before William and Kate were due to attend a service in her memory.

The extraordinary decision by Harry to show up unannounced seemed designed to undermine his brother’s carefully scheduled appearance in Wales, some 230 miles away, which began shortly after social media was flooded with pictures of Harry leaving the chapel.

The chapel is open to the public and it is thought Harry simply walked in.

It was the latest sign of the parlous low to which relations between Harry and the royals have sunk.

A spokesperson for the king, who has been keen not to escalate the conflict with Harry, declined to comment, but palace sources sought to transmit a sense of insouciance, saying that members of the royal family had “found ways to pay tribute at the chapel privately and individually” and implying the king had no issue with this.

Privately, of course, palace planners are likely to be rolling their eyes at what seems like a calculated attempt by Harry to upset the careful choreography of the day’s events. These saw the king issue a statement and audio message praising his mother on the stroke of midnight and then attend a church service Friday morning at Balmoral in Scotland, where he and Camilla greeted members of the local community.

William, however, is unlikely to be so relaxed or to miss the significance of his brother’s actions. Relations between the two brothers were strained by Harry’s departure from the family but descended to rock bottom after Harry published his memoir, Spare, in which he accused William of physically attacking him and belittling him, and also revealed private and intimate details about his wife, Kate.

Harry now lives in California with his wife, Meghan, but is in the U.K. for a series of charity events.

On Thursday evening he attended the WellChild Awards in London, where he said, “As you know, I was unable to attend the awards last year as my grandmother passed away. As you also probably know, she would have been the first person to insist I still come to be with you all instead of going to her, and that’s precisely why I know, exactly one year on, she is looking down on all of us tonight, happy we are together, continuing to spotlight such an incredible community.”

Immediately after his visit to his late grandmother’s tomb, the Daily Mail reported that Harry traveled to Heathrow airport and took a flight to Düsseldorf, where the Invictus Games open on Saturday.

The Mail reported that upon landing, he headed to the five-star Hyatt hotel, where he checked into the presidential suite.