PrimeStone was established in 2014 by three former partners from The Carlyle Group, specialising in buy-outs, and who have worked and invested together across Europe for more than 20 years. PrimeStone has a strategy of constructive and active management in mid-sized, listed, European companies that have significant value creation potential through strategic, operational or financial improvement. 
PrimeStone creates value by taking a long-term perspective, adopting an active approach and having a significant influence over its underlying investments through a constructive dialogue with boards and management teams. 

Sienna Capital & Primestone

As part of a long-term agreement, Sienna Capital invested EUR 150 million in February 2015. In exchange for its support of PrimeStone, Sienna Capital benefits from certain favourable financial terms. 


Investments which are quoted, listed or traded on or under the rules of a recognised market are valued at the closing price. 

Financial Year 2019 

The portfolio’s organic growth at constant currency was about 30%, with the fund’s largest investments, JSG and Spirent, performing well in 2019. 


Value of Investment (12/31/2019) 


Business area

Mid-sized European Equities  

Registered office

London, UK

Key Data from GBL Annual Report 2019 


Martin Donnelly 
Chief Operating Officer