Alexandre Gaydamak has taken full control of Portsmouth having agreed a deal for chairman Milan Mandaric's remaining shares.
Gaydamak arrived at Fratton Park in January as co-owner and has now bought out American-Serb businessman Mandaric, who will continue in his role as non-executive chairman of the club.
Mandaric told the club's website: 'This does not mean I am walking into the sunset. I will be here to help Alexandre Gaydamak in any way I can and also maintain my friendship with the wonderful supporters.'
Gaydamak's investment was felt immediately in the new year when manager Harry Redknapp made a host of signings to save the club from relegation.
That spending power has increased this summer with Glen Johnson arriving on loan from Chelsea and a number of signings set to follow, reportedly including Benfica midfielder Manuel Fernandes for £10million.
French businessman Gaydamak told the club's website, pompeyfc.co.uk: 'What Milan has done for this club is priceless.
'Milan is the reason the fans are here and is responsible for me tying the knot with Pompey.
'Milan's vision, belief, hard work and compassion has laid the entire foundation for all that we started to do in January this year, are working on at present and intending to do in the future.
'Following in these footsteps is not easy and I do so with pride and great admiration.
'No club could have wished for a better owner and no club could have a better chairman.'
Jermain Defoe, Aiyegbeni Yakubu, Nicolas Anelka, Jefferson Farfan and Sol Campbell have all been linked with Pompey as Gaydamak's money burns a hole in their pockets.
Mandaric always maintained he would only pass on control to someone who had the club's best interests at heart and believes now is the perfect time.
'I could not have asked for a better scenario than this one and I know that supporters are going to give Alexandre the same wonderful backing and encouragement they gave me.
'I can do this all safe in the knowledge that I will place Portsmouth Football Club in the control of a person that has massive ambitions, who has fallen in love with the supporters and is someone who will take this on to the next level.
'I can look back with a great deal of satisfaction on what this club has become today but this is now the beginning and a time to look forward with intense optimism and excitement.'