Slobodan Zivojinovic of Yugoslavia in 1988. Photo / Getty Images

A Serbian tennis player has claimed he had a relationship with Princess Diana while she was married to Prince Charles.

Slobodan Zivojinovic, 52, said the relationship began in the late 1980s when the princess watched him play at Wimbledon, after which they became "extremely close".

The sportsman, who was engaged at the time, claimed Diana would watch him play from the courtside stands rather than the VIP seats so she could be closer to him.

Speaking to a Serbian newspaper, Zivojinovic said he first met the royal before a Wimbledon match in 1987. "In our first conversation she asked me if I am the tennis player with the fastest serve and I said, 'yes'," he said. "Then she asked if my serve was still good. Shortly after that we started seeing each other."

Zivojinovic - who became the first Serbian world number one doubles player in 1986 - said the relationship continued even though he was with fiancee Zorica Desnica, and Diana was married to Prince Charles. The tennis star added: "She was a wonderful woman. With her I could talk about everything and even simple things became fascinating.

"I don't want to speak about it in any detail now that she is no longer with us. What I can say is that it is great when someone like her comes to watch the match and supports you. Never happened to me before that someone from the royal family came to support me."

Zivojinovic retired in 1992, the year after he married his current wife Lepa Brena, a folk singer. The 6ft 6in player represented Yugoslavia at the 1988 Olympics in Seoul, South Korea. He reached his highest singles ranking in 1987, when he became world number 19.