The owner of Phar Lap's 1930 Melbourne Cup hopes to see the famous racehorse reunited with his most famous prize.

Lady Susan Renouf says it would be ideal for the gold cup to be side by side with Phar Lap's hide, which is displayed at the Melbourne Museum.

"I think my family may have something to say about that, but I think the two should be together," she said.

For now, the 18-carat gold cup will hold pride of place in the National Gallery of Victoria's new exhibition, The Horse.

The display is the first public showing of the cup, which was thought lost before racing historian Andrew Lemon concluded it had most probably been rebadged twice - in 1953 and 1980.

The race in 1980 was won by Lady Renouf and then-husband Robert Sangster with Beldale Ball.

Dr Lemon said only 12 cups were made to the exact design of the 1930 cup and closer inspection had made it almost impossible that the 1930, 1953 and 1980 cups were not the same trophy.

Phar Lap's owner Harry Telford sold the 1930 cup for its gold when in financial difficulties in the 1940s.

High gold prices forced the Victoria Racing Club to use an old cup for the 1953 race and they repeated the process in 1980.

"We've never been able to 100 per cent prove that it was Phar Lap's cup, but that is the logical conclusion," Dr Lemon said.

"It is amazing to think ... some horses are ordinary and they have ordinary cups and ordinary stories, and then there's Phar Lap who keeps on hogging the myth by having this mystery cup," he said.

The cup will remain on display until November 8.