The Kylie Vella-trained Admiral's Joker has returned a positive result to a non-steroidal anti-inflammatory after winning a race at Flemington on Andrew Ramsden Stakes day.

Six-year-old gelding Admiral's Joker won an 1800m handicap on the May 25 program.

Racing Analytical Services Limited said Admiral Joker's post-race urine sample showed the presence of Diclofenac, a prohibited substance under the Australian Rules of Racing, while the Australian Racing Forensic Laboratory also detected the substance in the reserve portion of the sample.

Vella was told by Racing Victoria stewards of the irregularity on July 5 before being told of the confirmatory findings on Tuesday.

Stewards are continuing their investigations.