JAKARTA, Apr. 23 (Reuters) - Indonesia President Joko Widodo and his son, incoming vice president Gibran Rakabuming Raka, are no longer members of the country's largest party after they backed rival candidate and election winner Prabowo Subianto, a party official said on Tuesday.

Their exit will put the spotlight on the next moves for the popular Jokowi, as the outgoing president is known, whose backing for Defence Minister Prabowo was widely interpreted as a move to retain political influence and preserve his legacy after a decade at the helm.

Komarudin Watubun, who heads the ethical division of the Democratic Party of Struggle (PDIP), said Jokowi and Gibran were not expelled but ceased to be members when they decided not to endorse PDIP's presidential candidate Ganjar Pranowo.

Helped by Jokowi's tacit endorsement and with Gibran as running mate, Prabowo won by a huge margin in the Feb. 14 election, taking 58% of the vote compared to Ganjar's 16%.

"They decided to be on the opposite side," Komaruddin told Reuters. "Regardless of what happened, Jokowi reached the highest career level in the party, he has become president. We want to preserve his dignity," he said.

The president's office did not immediately respond to a request for comment.

Jokowi joined PDIP in 2004 to run for mayor of Surakarta and won two terms. He was later elected Jakarta governor and became president for two terms with PDIP's backing. Gibran has also served as Surakarta mayor since 2020.

Jokowi's backing of Prabowo has created tension between him and PDIP, which will remain the biggest party in parliament following the election.

Jokowi has yet to discuss his political plans but according to several sources, he wants to take over the second-biggest party, Golkar, a move that could see him retain sizable influence and potentially counterbalance that of old rival Prabowo when he takes office in October.

Prabowo's current coalition comprises 48% of seats and senior aides have said he aims to expand that to command a majority. Several parties, such as Nasdem, which backed another candidate, have already held talks with Prabowo.

Speculation is also rife that PDIP chairwoman Megawati Sukarnoputri, a political heavyweight, could soon meet Prabowo to discuss joining his coalition amid the ongoing rift with Jokowi.

Photo from Reuters