Eric Idle has no sympathy for Nick Reiner as he fights to access family money for his murder trial defense ... and the reason is deeply personal.

We got the "Monty Python" legend out in NYC Monday and asked how he felt about Nick trying to use some of the family's fortune to pay his attorney.

Eric's answer was short and brutal ... "I was the last man probably to talk to his father, so I have no sympathy."

As TMZ previously reported, Eric spoke with Rob Reiner for more than an hour the night before Rob and his wife, Michele, were killed in their home.

Eric later paid tribute to his longtime friend on X ... calling Rob a "lovely man" and saying they discussed filming, the future and plans to see each other again.

Rob and Eric were friends for 50 years.

Nick has pleaded not guilty to two counts of first-degree murder in his parents' deaths. He's been fighting for access to his trust money, which he says he needs to pay for a private defense attorney.

His legal team recently claimed he's owed $558,000 and argued at least $325,000 came from his grandfather Carl Reiner -- money they say should not be blocked under California's Slayer Statute.

For Eric, though, the money fight doesn't change a thing.