Zara Tindall was pictured at Cheltenham as fans issued a rallying call for the royal to "support Prince William".
The mother-of-three, 42, is not a working member of the Royal Family, and instead works as a professional equestrian.
Zara, who married rugby player Mike Tindall in 2011, stepped out at the Cheltenham Festival on Thursday alongside her husband.
This came as several members of the Royal Family have temporarily halted duties, including King Charles, Princess Kate and Prince William.
Zara and Prince William are first cousins
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The King and the Princess of Wales are both battling cancer, while William is undertaking a reduced public role while he cares for his wife and family.
Royal fans took to social media to issue a rallying call for Zara, who was raised without a title, to become a working member of the family.
One fan compared Zara to her mother Princess Anne, 73, in her support for King Charles, and claimed Zara could provide that support for Prince William during his reign.
They wrote on social media: "Zara Tindall would be an absolutely excellent choice to join the working royals and support William, just as Princess Anne has supported her brother Charles admirably and loyally for decades!
Mike Tindall and Zara Tindall photographed at Cheltenham on Thursday
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"I wish them well and for it to all work out great."
Another fan wrote about Mike and Zara: "I so want them to become working royals. What a great addition they’d be."
A different social media user added: "Zara and Louise are great choices as potential working royals," referring to Zara's cousin Lady Louise Windsor, 20.
Similarly, someone said: "I think Zara and Mike would be perfect as working royals.
Zara Tindall looked beautiful during her outing at Cheltenham
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"They are popular and fun, and loyalty is proven."
A royal watcher commented: "It would be great for the Royal Family if Zara was a working royal. She’s the eldest of the late Queen's grandchildren.
"Princess Anne gave none of her children titles. Zara would be a brilliant asset."
Another social media user pointed out the current shortage of working royals, posting: "Having Beatrice, Eugenie, Zara, and Mike as working royals is necessary for the next generation."
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There are calls for Mike Tindall and Zara Tindall to step up as working royals
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Finally, someone said: "Lady Louise, Zara and Mike Tindall are good suggestions to become working royals in my opinion."
Zara looked fabulous for her outing at Cheltenham, choosing a £625 trench coat from Fairfax & Favor.
She accessorised with a £550 handbag from Aspinal of London and a £139 headband from Camilla Rose Millinery.
The mother-of-three further accessorised with £150 Finlay sunglasses and donned £429 LK Bennett boots.