Gov. Deval Patrick said his endorsement Thursday morning of attorney general candidate Warren Tolman stemmed from his personal connection to Tolman.

"Warren's been a friend, and a close one, for a very long time," Patrick said on his monthly appearance on WGBH News' Boston Public Radio. "He played a very special role in my re-election campaign, both on- and off-camera, mostly off-camera. He and his team were relentless."

Patrick acknowledged the unusual nature of the endorsement, which took many observers by surprise.

"I'm supposed to stay out of contested Democratic primaries and I try to," he said. "I think both of these candidates are so good."

He went on to praise Tolman's opponent, Maura Healey, who had been described by hosts Jim Braude and Margery Eagan as similar to a young Deval Patrick.

"Her work on the [Defense of Marriage Act] issue in particular is something that's deeply meaningful to me," he said.

Despite today's move, Patrick said there will be no forthcoming endorsement in the governor's race.

Listen to the full interview on Boston Public Radio below: