Former agency exec headed ad unit

Brian Lesser, who headed AT&T’s Xandr advanced advertising unit, suddenly resigned his post, according to reports.

Xandr was part of AT&T’s effort to monetize its big investment in television and media properties including DirecTV and Time Warner.

The departure was first reported by Reuters. A Xandr spokesman did not return calls.

Lesser joined AT&T three years ago from media buying giant GroupM.

Lesser’s resignation reportedly was prompted by discussions that indicated that he would not be named to succeed John Stankey as CEO of WarnerMedia. Stankey was named COO of AT&T last year and had been holding down both posts.

Xandr had been buying companies in order to boost its advanced advertising capabilities including AppNexus and Clypd.

On Wednesday the company announced that The Walt Disney Co. and AMC Networks had agreed to use the Xandr Invest platform to target commercials on their linear TV networks, a major coup fo the company.