The Princess Royal, 70, is widely thought to be the most hard-working royal. Royal commentator Richard Fitzwilliams said it must be “frustrating” for Anne with the current lockdown.
Mr Fitzwilliams told Express.co.uk: “She is a hard worker.
“I think it must be a particularly frustrating time for her at the moment because she’s in lockdown at Gatcombe Park.
“As she said in that documentary which marked when she was 70, sitting still really doesn’t happen very much, so she does find it frustrating.
“She’s been carrying out engagements virtually and by telephone, I understand, for various charities.”
“Of course, we think back to her successes in the equestrian field.”
Anne is already a grandmother to Zara and Mike’s two children Mia, seven, and Lena, two.
She is also a grandmother to Peter and Autumn Phillips’ children, Savannah, ten, and Isla, eight.
Mike revealed he and Zara were expecting their third child during an episode of The Good, The Bad & The Rugby podcast in December.
The ex-England rugby player told co-hosts Alex Payne and James Haskell: “It’s been a good week for me, had a little scan last week – third Tindall on its way.”
When asked about the baby’s due date, Mike said: “We like to play our cards close to the chest.”
In December, a source claimed equestrian Zara was four months pregnant.
The insider told the Telegraph: “Zara is four months pregnant and they are absolutely delighted to be able to share this news.”