Pompey have signed Croatian goalkeeper Petar Durin from Italian Serie A club Atalanta for an undisclosed fee, subject to international clearance.
The 17-year-old has penned a two-year deal at Fratton Park, with a club option for a further 12 months.
Durin – who has represented his country up to under-18 level – said: “I’m very pleased to be here and to have the chance to play for such a big, big club.
“Now I need to work hard and make sure that I can repay the trust that Pompey have shown by bringing me here.”
Dave Wright, the Blues’ Head of Academy Performance and Recruitment, said: “This is a big step forward for the club, investing in a young player with a lot of promise.
"This is a big step forward for the club, investing in a young player with a lot of promise."
“To my knowledge, it is the first time for many years that we have paid a transfer fee for a youth team player and that is a sign of the long-term intent of our board.
“After liaising with Atalanta and arranging for him to train with us, we immediately felt he had all the attributes required to go a long way.
“John Keeley, our goalkeeping coach, advised us how good he believed Petar was – and, as importantly, how good he could be – and we are very excited that he has chosen to sign for us.
“We felt straight away that he was someone we wanted to bring to the club and after lengthy negotiations with Atalanta and backing from our board, we’re delighted to finally sign him.”