The former secretary general of the now-defunct Herbert Smith alliance, Olivier Clevenbergh, is set to leave Benelux firm Stibbe to launch his own boutique.

Clevenbergh, who was secretary general of the decade-long alliance between Herbert Smith, Stibbe and Germany's Gleiss Lutz from July 2011 until the relationship officially ended in December last year, handed in his notice last week.

Clevenbergh will open a corporate and litigation boutique in the coming months with between three and four partners from other firms. The names of the partners and an exact launch date are yet to be announced. The new firm will give Belgian law advice to large and mid-size Belgian and foreign companies.

Clevenbergh was also previously managing partner of Stibbe's Brussels arm from January 2005 until June 2011.

He said: "I had much excitement while I was managing partner and then secretary general, and while I really enjoy client work, I wanted to do something more.

"At this stage in my career it's now or never to start a new firm and I thought it would be a fantastic challenge, particularly in light of the fact that there is a space in the market for this type of boutique right now because it can offer greater flexibility than a large firm while offering the same quality."

The firm is expected to grow to around 40-50 lawyers, including about 10 partners, over the coming years. The boutique will not be named after any of the partners.

The news comes after Gleiss and Stibbe rejected Herbert Smith's proposal to merge in November last year, leading to the formal dissolution of the alliance in December 2011.

Following the move, Stibbe announced this month that it will open a Hong Kong office in September this year, in a bid to expand its global presence.