Mark Hughes has been appointed as the manager of Southampton until the end of the season.
The 54-year-old will take his first training session on Thursday with Mark Bowen and Eddie Niedzwiecki joining his backroom coaching staff as assistant manager and assistant first team coach respectively.
Hughes, who made 60 appearances for the club, said: "It's a challenge I'm excited by. It's a great opportunity to come back to a club I know well, and a club I've got a real affinity with, and I couldn't turn that down.
"I bring experience of the Premier League. I understand what it takes in this league to win games. But first and foremost I think it's about coming in and maybe being that different voice, that different message from myself and the staff, that will enable the players to recognise and focus on what needs to be done in this key period of the season.
"The objective clearly is to remain in the league and make sure we're a Premier League club next year."
Hughes was dismissed by Stoke City in January, with the Potters in the bottom three following a poor run of form. But they had three ninth-place finishes under the Welshman before finishing 13th last term.
Hughes began his managerial career with the Wales national team and subsequently managed Blackburn, Manchester City, Fulham and QPR. He has never been relegated from the top flight as manager.
Pellegrino was sacked on Monday after just one win in their last 17 games - leaving the team just a point clear of the relegation zone.
Hughes' reign as Southampton boss begins with an FA Cup quarter-final tie against Wigan at the DW Stadium on Sunday.