"How good was the meeting with @POTUS?" Graham tweeted after the lunch. "I gave him my NEW cell phone number."
Trump famously read Graham's personal cell phone number out loud to hundreds assembled for a South Carolina campaign rally in July 2015.
Graham laughed it off at the time, tweeting, "Probably getting a new phone. iPhone or Android?"
He later made a video for conservative-leaning website Independent Journal Review, using a machete, blender, lighter fluid, golf club, concrete block, bat and toaster oven to destroy his signature flip phone.
But on Tuesday, it was clear that the Republicans were newly committed to working together.
"I had a great lunch meeting with President Trump today. He is strongly committed to rebuilding our military which is music to my ears. President Trump is in deal-making mode and I hope Congress is like-minded," Graham said in a statement Tuesday afternoon.
In the daily briefing, White House press secretary Sean Spicer called Graham an "important partner" as the White House works with the Senate to confirm Supreme Court nominee Neil Gorsuch.
The two traded their fair share of jabs throughout the primary; even after Graham suspended his presidential campaign, he was a vocal critic.
During that same July rally in South Carolina, Trump called the state's senior senator an "idiot." Graham had called Trump a "jackass" earlier that week in an interview
with CNN's Kate Bolduan.
When Graham spoke out against Trump's candidacy in March 2016, Trump tweeted, "Failed presidential candidate Lindsey Graham should respect me. I destroyed his run, brought him from 7% to 0% when he got out. Now nasty!"
Trump also called the South Carolina senator a "nasty, angry, jealous [failure]" with "ZERO credibility."
As recently as late January, Trump called Graham and Sen. John McCain "weak on immigration."
For his part, Graham, who initially endorsed Jeb Bush and then Ted Cruz, called Trump "completely unhinged," citing the then-candidate's insinuation that Sen. Ted Cruz's father was involved with Lee Harvey Oswald in the JFK assassination.
Hours before the Indiana primary polls closed in May and Cruz dropped out, Graham tweeted: "If we nominate Trump, we will get destroyed.......and we will deserve it."
And one month before election day, Graham wrote: "I have never been comfortable with Donald Trump as our Republican nominee."
Whether the President keeps Graham's new phone number to himself remains to be seen.