Obama, Hillary Clinton sit down to lunch

Updated at 2:46 p.m. ET on 7/29

(CNN) – As the nation's top diplomat, Hillary Clinton used to be a regular presence at the White House, but since leaving her post as secretary of state earlier this year, Clinton has been busy delivering speeches and launching her post-government initiatives.

On Monday, however, Clinton made a return to the building for lunch with President Barack Obama.

Plenty of issues – ranging from health care to Middle East peace talks – could have been conversation starters for the pair, though on Monday, Deputy Press Secretary Josh Earnest said it was "largely friendship that's on the agenda for the lunch today."

"Much has been written about over the last four years how Secretary Clinton and the president have developed not just a strong working relationship, but also a genuine friendship," Earnest said, adding the lunch was an "opportunity for the two, who saw each other on a pretty frequent basis over the course of the last four years, to have the chance to catch up."

Clinton will also meet with Vice President Joe Biden Tuesday at his residence, the Naval Observatory, Clinton aides, as well as a White House official, told CNN. One person with knowledge said the meeting was "long scheduled."

As for her Monday meeting with Obama, Earnest said the president invited Clinton to the lunch, which had grilled chicken, pasta jambalaya and salad on the menu.

Current Secretary of State John Kerry was spotted arriving at the White House around the same time as Clinton, though Earnest said he believed Kerry did not join his predecessor and Obama for the lunchtime meeting. Clinton, however, did stop by to say hello while Kerry met with National Security Adviser Susan Rice, according to Clinton aides.

The White House is preparing for Middle East peace negotiations in Washington Monday night, and Earnest indicated it was more than possible that the talks could have come up come during the meal.

"The purpose of the lunch was chiefly social, but given that the president and Secretary Clinton worked on this pretty closely together over the course of the last four years, I'd be surprised if they didn't," he said.

According to Clinton aides, the lunch came together when Obama and Clinton saw each other at the George W. Bush Presidential Center dedication ceremony in April, where Obama and former President Bill Clinton gave brief remarks. With the president and the former secretary of state having busy schedules this summer, July 29th became the agreed upon date, the aides said.

Former rivals during their marathon battle for the 2008 Democratic presidential nomination, Obama and Clinton forged what most parties say was a strong working relationship during her years at the State Department. Since her departure, the pair met for dinner at the White House along with her husband, and for the dedication of the Bush library in Texas.

Clinton, a potential candidate for the White House in 2016, has spent her months post-State appearing at events focused on women's empowerment, as well as maintaining a healthy roster of paid speaking engagements.

She launched an initiative through the Clinton Foundation dedicated to early childhood development, and signed a book deal in April for a diplomacy-centered memoir to be released in 2014.

CNN's Jessica Yellin, Kevin Liptak and Ashley Killough contributed to this report.