In her 2008 classic song Love Story, Taylor Swift fantasised about getting proposed to: "He knelt to the ground and pulled out a ring / And said, 'Marry me, Juliet.'"

Seventeen years later, Swift, 35, finally had her fairy-tale engagement. The football player Travis Kelce, also 35, proposed with what appears to be an elongated, old mine cushion cut diamond set on a yellow gold band. (A cushion cut diamond has rounded corners.)

The ring was designed by Kindred Lubeck of Artifex Fine Jewellery in New York. Lubeck makes hand-engraved jewellery with natural gemstones.

"It's not just a flashy piece, but more of an aesthetic, really beautiful diamond," said Marion Fasel, a jewellery historian and the author of The History of Diamond Engagement Rings: A True Romance. Her friends in the jewellery world, she said, have been excited about the piece because of its high quality.

"You can tell this is a beautiful diamond from the light and faceting arrangement," Fasel said, estimating the weight to be around 7 carats.

Many celebrities have sported giant rings this summer, including Georgina Rodríguez, who got engaged to Cristiano Ronaldo in August; Chioma Rowland, who was married to the Afrobeats star Davido in August; and Lauren Sánchez Bezos at her wedding in June. But the size of Swift's rock came as a bit of a surprise to Fasel. "I thought she would have a stone we could see, because she's a showgirl," Fasel said. "But not something quite this big."

But, Fasel said, the ring is not out of scale: "It's in proportion to her hand. She has long fingers, and it goes up the finger beautifully. It's large, but it's not so large that it's vulgar." There also appears to be engraving on the side, as well as two smaller diamonds. "They must mean something, because everything with Taylor means something," Fasel said.

Ann Grimmett, the vice-president for merchandising at Jared Jewellers, estimated that the diamond was seven to nine carats, costing anywhere from $250,000 to $500,000. "Taylor Swift's ring has an heirloom look that is both romantic and dreamy," Grimmett said.

Nilesh Rakholia, the founder of Abelini Jewellery, a British jewellery brand, estimated that the ring weighs seven to 10 carats, costing between $1 million and $1.3 million.

"What makes this design particularly striking is its blend of vintage charm and modern minimalism," Rakholia said. "The choice of yellow gold has been making a huge resurgence in fine jewellery, loved for its warmth and ability to enhance the brilliance of white diamonds."