Rosenthal joined Signia from Amundi Alternative Investment in 2013. The group said he grew Amundi’s hedge-fund assets from £1.2bn to £28bn in his eleven-year tenure there.
French national de Merlis initially joined Signia’s investment team in 2011 before leaving to set up an asset manager for entrepreneurs and their families, but he rejoined the firm in 2015.
Signia did not state a reason for his second departure.
The firm manages investment portfolios for individuals, trusts and institutions and offers tax and wealth structuring in addition to offering traditional long-only portfolios, hedge funds and private equity.
Rosenthal said in a statement: “I believe that we are at an interesting juncture in markets and that the investing environment is likely to become more challenging over the coming period.
“I am confident that with Signia Wealth's talented team and our extensive investment experience, we will be able to add significant value for our clients across all asset classes.”