Pompey have signed Anton Walkes from Tottenham for an undisclosed fee.
The versatile 21-year-old – who spent the second half of last season on loan at Fratton Park – has penned a two-year deal, with the club holding an option for a further 12 months.
Walkes previously featured at both right-back and in midfield, and has been handed the number two shirt.
Blues boss Kenny Jackett said: “He’s somebody we obviously know very well and he had a successful loan spell with us in a number of positions.
"Anton’s still young and has a really big future in the game, so we’re delighted to be able to sign him on a permanent basis."
“When he got injured towards the end of the season, we missed him greatly and so we’re pleased to bring him back.
“Anton’s still young and has a really big future in the game, so we’re delighted to be able to sign him on a permanent basis.
“I’m looking forward to him rejoining the group and getting some minutes on the pitch at Swindon on Saturday.”
Walkes scored on his Pompey debut in a 2-2 draw against Doncaster after arriving on loan back in January.
He played a total of 12 times as the Blues narrowly missed out on a place in the League One play-offs.
Walkes is a graduate of Tottenham’s academy and made a single senior appearance for the Londoners, while also enjoying a spell on loan with MLS outfit Atlanta United.