Heidi Agan makes her living as a Kate Middleton impersonator, so as Middleton's belly grows during pregnancy, so must Agan's.
Agan, of Northamptonshire, England, reportedly bought a number of belly prosthetics to recreate the look of a pregnant Duchess of Cambridge.
According to the BBC, the Middleton look-alike said she bought a "bump in various sizes."
Explaining her decision, she said: "As Kate grows I will, too - to be authentic I thought it was important."
Agan, 32, has two children. She made headlines last year when she quit her waitressing job to be a full-time Middleton impersonator, commanding more than $1,000 per appearance.
In her efforts to be as authentic as she can, Agan has appeared in clothing Middleton has popularized, including the blue Issa dress Middleton wore when she and Prince William announced their engagement in 2010 and a replica of the Sarah Burton for Alexander McQueen dress Middleton wore on her wedding day in April 2011.
Middleton, 31, is married to Britain's Prince William. She is carrying their first child.
Their baby, whose gender has not been revealed to the public, is due to be born in July.