Vin Diesel broke down in front of Paul Walker's mother

Vin Diesel was so devastated at the death of his close pal Paul Walker, he broke down in front of his Fast & Furious co-star's grieving family.

Walker was killed in a fiery car crash earlier this month (Dec13) when a Porsche driven by his friend slammed into a pole, killing both driver and passenger.

In an emotional Facebook post, Diesel reveals he flew to California to visit Walker's family to offer his support as soon as he heard about the tragedy, but he ended up being comforted by Walker's mother.

He writes, "When I heard, I immediately flew back to California, and went directly from the plane to his mother's house...I thought they needed my strength, but realized (sic) when I got there and broke down before his family, that it was I who needed theirs. His mother hugged me and said I am so sorry... I said sorry? You're the mother who lost a son?... She said yes, but you lost your other half..."