Hopes of a Gold Cup repeat for Estimate at Royal Ascot have risen markedly after the Queen's mare shone in a piece of work in Newmarket.

The five-year-old has only been seen once since her famous triumph 12 months ago when she became the first horse running in the colours of a reigning monarch to lift the historic staying championship.

Her trainer Sir Michael Stoute admitted earlier in the week that a setback had hindered her progress but he was expecting a bold defence of her crown.

Estimate and Ryan Moore worked with Hillstar on the Al Bahathri Polytrack on Saturday.

"She's not as tuned as last year with the Sagaro run, but then she's with a master trainer," the Queen's racing manager John Warren said.

"Sir Michael rang me to say she had done a really nice piece of work.

"She did a serious piece about ten days ago and needed a couple of pieces of fine-tuning, but he said 'we're where I need to be'."

Trainer Marco Botti says Tac De Boistron will not take his place in the race if he considers the ground too fast for the seven-year-old who won the Sagaro Stakes impressively over the course on soft ground in the spring.

"I've checked the forecast and there's no rain at all on the cards, but they did have some last night," Botti said.

"We will monitor the ground. If it's good to firm I don't think he'll run. We would like to run, but it depends on the ground."

Tac De Boistron had a campaign in Australia in 2012 with Mick Kent but was unplaced in the Geelong and Melbourne Cups in which he struggled on the firm tracks.