kate middleton
Ava Watt, aged 9 with Cystic fibrosis, presents Catherine, Duchess of Cambridge with a gift during her visit to Great Ormond Street Hospital on January 17, 2018 in London, England Getty

The pregnant Duchess of Cambridge has grown out of her sapphire engagement ring due to swollen hands.

The 36-year-old Kate Middleton was forced to leave her £300K blue sparkler at home, which once belonged to the late Princess Diana, as she paid a visit to Great Ormond Street Hospital this morning (17 January).

Mixing up her style, the duchess opted for a chic red coat from high street store Boden, which retails at £220, in contrast to her £1,500 pink Mulberry coat worn in Coventry with husband Prince William yesterday.

Kate completed the vibrant look with her trusty black court shoes and a small black clutch, accessorising with a pair of pearl drop earrings to compliment her elegant Chelsea blow-out.

The royal visited the children's hospital to open the latest phase in the institution's ambitious redevelopment project. She is scheduled to meet young patients and their families to hear about their experiences of the enhanced facilities in the completed Mittal Children's Medical Centre.

The centre has transformed the hospital's inpatient facilities and provides modern accommodation for all patients, also letting parents or carers stay comfortably by their bedside.

kate middleton
kate middleton

In her speech, she congratulated the centre, stating: "It's been wonderful to meet so many families and young people. I've been so inspired by their bravery and courage at such a difficult time."

Kensington Palace tweeted: "The Duchess joins some children for an art activity, and discovers more about the positive impact the new centre is having on @GreatOrmondSt patients & their families.

"The children have been able to move into new, modern wards where parents or carers can stay comfortably overnight by their child's bedside."

kate middleton
Catherine, Duchess of Cambridge during her visit to Great Ormond Street Hospital on January 17, 2018 in London, England Getty

Kate – who is expecting her third child with William in April – will also meet staff caring for young patients during the daytime engagement, as well as talk to clinicians carrying out cutting-edge research to help seriously ill children.

The duchess, a patron of the All England Lawn Tennis and Croquet Club, will later visit Bond Primary School in Mitcham, south London, to view the work of the Wimbledon Junior Tennis Initiative.