The Queen has arrived at Sandringham House in Norfolk ahead of her 96th birthday.
Harry said his grandmother was "on great form" after they met at Windsor Castle, before he travelled to Holland for the Invictus Games.
But he pointedly added in an interview with NBC that he wanted to make sure she was "protected" and had "the right people around her".
The Queen has been experiencing mobility issues in recent months and has cancelled appearances at a number of high profile events, but she did attend Prince Philip's memorial service and has continued hosting virtual events.
She will celebrate her 96th birthday on Thursday and is likely to be visited by family and friends in the coming days.
The monarch arrived at Wood Farm, the Duke of Edinburgh's cottage at Sandringham, where she is expected to stay.
Prince Philip lived in the cottage after retiring from public life, a property the Queen said her late husband "loved" partly because the "sea was so close".
The Queen commented on the cottage when she hosted a rare public event at Sandringham on February 5, the eve of her Platinum Jubilee.
Teresa Thompson, 70, the retired housekeeper of Wood Farm, said after chatting to the Queen that day: "All the Royal family love Wood Farm, because it's out of the way, it's small, it's intimate. You haven't got lots of officials and household, it's just the close staff.
"And they literally can relax in the family house, it's wonderful, and I had a wonderful 22 years down there, it was the best time of my life without a doubt."