TellApart CEO Josh McFarland is leaving Twitter for VC firm Greylock

Just a few weeks after Twitter finally hired someone to lead all of product, the company is losing another key product executive: Josh McFarland, who joined Twitter when it acquired his ad tech startup TellApart a little more than 18 months ago, is leaving the company.

McFarland is joining venture capital firm Greylock, which was one of the main investors in TellApart before he sold it to Twitter for more than $500 million back in April of 2015.

TellApart’s technology was intended for ad retargeting and cross-device tracking, but at Twitter, McFarland’s role and responsibilities expanded outside of ad tech shortly after the acquisition.

Following Twitter layoffs and a company-wide reorg in late 2015, McFarland took over all of Twitter’s customer service product initiatives, which were near the top of the company’s priority list. That meant he oversaw products related to contacting or messaging businesses that wanted to use Twitter for customer service purposes. At the time, it felt like Twitter was gearing up to push a new enterprise-friendly agenda, though it won the rights to stream a few NFL games a few months later and the focus seemed to shift toward those efforts instead. (Facebook’s foray into customer service Messenger bots hasn’t helped.)

Now, less than two years after TellApart’s acquisition, McFarland is leaving.

At Greylock, McFarland will be an investment partner. Current Greylock partner James Slavet told Recode he’s been recruiting McFarland to join Greylock since his days working on product at Google. He actually incubated TellApart as an entrepreneur-in-residence at Greylock back in 2008.

Slavet invested and joined TellApart’s board, and the two have stayed in touch since the Twitter deal.

McFarland is set to join the firm at the end of Q1 2017 and will invest out of the new $1 billion fund Greylock announced in October.

This article originally appeared on Recode.net.