The stylish Welsh opera singer has said she was "thrilled" and "surprised" by Andrew's proposal, which took place last week.
Katherine and Andrew have kept their relationship out of the spotlight and the 36-year-old was only confirmed as Katherine's boyfriend in March when she was awarded her OBE from Prince Charles.
Katherine and Andrew at Buckingham Palace
The mezzo-soprano had Andrew firmly by her side as she stepped out at Buckingham Palace to receive the prestigious accolade from the first-in-line to the throne.
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Katherine's friends have said Andrew proposed on 17 April, but the couple waited until all their family members had been told before breaking the news officially.
Andrew works as a professor at New York University, where he graduated in 2000, and is also an accomplished sculptor, artist and filmaker.
The couple during a date in Soho, London
His most recent cinematic work is a film called Lullaby, which stars Amy Adams, Jennifer Hudson and Jessica Brown Findlay – who is best known for her role as Lady Sybil in Downton Abbey.
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"Katherine is very excited," a source told the Mail. "She loves how artistic and intelligent Andrew is. He is considering moving to the UK for her."
This is not the first time Katherine has been engaged, in 2011 she announced that she was to wed former Blue Peter presenter Gethin Jones. Following their split Katherine headed stateside and has resided in New York since.
Despite her time in the US, the Welsh songstress was recently unveiled as the latest famous supporter of VisitBritain and it's projects such as the Countryside is GREAT campaign.
Along with stars including Oscar-winning director Steve McQueen, Lewis Hamilton, Sir Richard Branson and Dame Vivienne,Katherine will lead a drive to attract international visitors to Britain.