Former Sergeant Glyn Gurner served in the Royal Welch Fusiliers in Crete, North Africa, Italy and Palestine for 10 years from 1936 but lost his service medals in the 1950s.
The grandfather was surprised with the replacements on his doorstep in New Tredegar, Caerphilly, by Regimental Sergeant Major Richie Davies, Goat Major Sergeant Mark Jackson and their regimental goat Fusilier Shenkin IV.
RSM Davies said: "Glyn signed up to the Royal Welch Fusiliers back in 1936 and served until 1946.
"I located his service documents in the South Wales Borderers Museum in Brecon and when I heard he had lost his medals in the 1950s I wanted to ensure he had replacements made up especially for his 100th birthday.
"It's an absolute privilege to do something for someone who served his country in the way Glyn did."
Major General James Swift, Regimental Colonel of The Royal Welsh, has written a letter of congratulations to the centenarian.
The letter said: "I know that you volunteered and joined 1 Welch well before the Second World War in 1936. Your service during the war took you to most of the hot spots - Crete, North Africa, Italy and Palestine.
"Like many of your generation you put your life on hold to serve your King and country. For those who have not served in uniform this is something that people of today do not quite understand, but for those serving in today's Army and your Regiment, we salute you and thank you for your sacrifice."
Mr Gurner said: "This is unbelievable. I never expected anything like this.
"What a wonderful thing to do. I can't believe I've got my medals back."
His son, Neil Gurner, said: "My dad is as fit as a fiddle. He never stops. This has really made his day and we'll never forget it."