Alongkorn will ask party members to support Pita’s bid to become prime minister, he said.
The Democrats made it clear to voters during the election campaign that they would heed the voice of the people, Alongkorn added.
"The Democrats will respect the people's vote by supporting Move Forward leader Pita Limjaroenrat as the next prime minister if the party gains the majority of votes in the House of Representatives," he said.
He will make a formal proposal to the party’s executive committee next week and will also discuss the party’s position with its members, Alongkorn said.
It is time for the Democrat’s to ensure a smooth transition in government that aligns with the people's will, he added.
The Democrats are ready to scrutinise the actions of a Move Forward-led government as an opposition party, Alongkorn said.
Move Forward won 152 seats – 113 constituencies and 39 party-list seats – in the May 14 election to emerge as the single largest party in the House of Representatives, according to unofficial results announced by the Election Commission.
Pita announced the day after the election that Move Forward would form a governing coalition of six political parties. Together, they will have a combined 310 seats in the 500-seat House of Representatives.
The Democrats, which are not among the six parties in the coalition, won 22 seats in the election.
Meanwhile, former House speaker and Democrat leader Chuan Leekpai said a comment he made on Tuesday had been misinterpreted and that he felt uncomfortable that inaccurate information had triggered conflict.
On Tuesday, he said: "Do not interfere with other political parties."
On Wednesday, he said the comment was not intended to criticise Pita.
Pita has not pressured political parties to choose him to be the next prime minister, Chuan said.
Political parties will decide on the candidate they will support for prime minister based on party consensus and the opinions of party executives, Chuan explained.
Chuan said that his, and his party’s reputation, had been damaged by social media users who posted a photo of him with a message saying: “He will join only with Caretaker Prime Minister Prayut Chan-o-cha, and other political parties are bad in his eyes.”
The Democrats are ready to be either a governing or an opposition party, Chuan said, reiterating previous statements.
“We should not think that we will only be a governing party. We must also be ready to be in the opposition," Chuan said, "We must have dignity in joining a coalition and not criticise political parties as being either good or bad."