Pte Prosser was a popular member of his battalion
A British soldier killed in an explosion in southern Afghanistan on Sunday was Private James Prosser, of the 2nd Battalion The Royal Welsh.
The Ministry of Defence said the 21-year-old, of Cwmbran, Torfaen, had been on vehicle patrol in the Musa Qal'eh district in northern Helmand province.
His family said James was "a wonderful son and brother" and spoke of their pride of "the man he grew to be".
His death takes the total number of UK soldiers killed in operations to 218.
Pte Prosser, a keen sportsman, joined the Army in July last year and was a popular member of the battalion which he became part of in February, the Ministry of Defence said.
Lieutenant Colonel Didi Wheeler, Commanding Officer of the 2nd Battalion The Royal Welsh, said: "He had a boundless sense of humour and was a true character in every sense despite his relative young age.
"This brave Welsh warrior will be sorely missed by so many of us."
Major Huw Jones, company commander, described Pte Prosser as "an astute and selfless soldier who always put his fellows ahead of himself".
"A brave professional, his passing has left a huge hole," he said.
Lt Tom Richards, 2 Platoon Commander, said: "It is rare that a big character's charisma is matched by professionalism, but Pross was one of those fortunate people who could naturally balance the two; he was quite rightly regarded by all as a model, though very junior infantry soldier.
"Pross died when he was 21; far too young to have either enjoyed properly what life had to offer him, or fulfil the potential he clearly possessed.
"The grief felt by his mates in 2 Platoon is great, and the void left in our lives can never be filled, but it is his parents and siblings that we now hold in our thoughts and prayers."